当前，我国对外开放面临的国际形势发生了新的变化，世界百年变局和世纪疫情交织，单边主义、保护主义抬头，经济全球化遭遇逆流，国际环境更趋复杂严峻和不确定。在此背景下，我国进口企业面临严峻的挑战，如何保持进口稳定以及保障企业的发展就是一个重大现实问题。我国政府高度重视优化国际市场布局的问题，提出要以企业为主体，创新开拓方式，拓展多元化国际市场，强调在深耕传统市场的同时，也要不断拓展新兴市场，促进外贸稳中提质和经济平稳运行，实现更高质量的发展。企业的进口市场转换行为是优化国际市场布局的重要方式。基于此，本文聚焦“进口市场转换”这一重要现象，针对中国企业的进口市场转换行为及其作用进行深入研究，在构建进口市场转换分析框架、分析进口市场转换特征事实的基础上，分别从进口维度、出口维度和创新维度三个方面对中国企业进口市场转换的作用进行深入研究，试图为我国进口企业通过自我调整实现高质量发展探索出一条新路径。

本文由7章构成。第1章为绪论。第2章为文献综述。第3章为进口市场转换的分析框架与特征事实，在构建进口市场转换分析框架的基础上，多角度描述了中国企业进口市场转换的特征事实。第4章为进口市场转换对中国企业进口稳定的影响，探究了外部不确定性增加情形下企业转换进口市场维持进口稳定的效应和渠道。第5章为中间品进口市场转换对中国企业出口韧性的影响，考察了中间品进口市场转换对企业-目的地出口韧性的影响效应和机制。第6章为进口市场转换对中国企业创新的影响，分析了进口市场转换方向和进口市场转换模式对企业创新的影响。第7章为研究结论与政策建议。

本文主要的研究内容和研究结论如下：

（1）中国企业进行进口市场转换的特征事实

在此部分，本文首先构建了进口市场转换的分析框架，界定了进口市场转换的含义，分解了进口市场转换对进口额的贡献，构建了进口市场转换率，并进一步界定了进口市场转换路径、转换方向和转换模式；其次，从多个角度描述了中国企业进口市场转换的特征事实。

统计分析的部分结果是：①多市场进口企业是我国企业进口的主导力量，历年平均值数据表明，多市场进口企业占全部进口企业个数的58.72%、占全部企业进口总额的96.30%。②进口企业转换进口市场的行为普遍存在，转换进口市场企业是我国进口的主导力量，多市场进口企业转换进口市场的行为更为突出，历年平均值数据表明，全部进口企业中大约有76.29%的企业转换进口市场，其进口额占比为96.30%，多市场进口企业中大约有92.43%的企业转换进口市场，其进口额占比为97.97%。③从进口市场转换率来看，多市场进口企业的进口市场转换率明显高于全部进口企业的进口市场转换率，历年平均值的统计结果表明，全部进口企业的进口市场转换率为0.56，多市场进口企业的市场转换率为0.61。④从进口市场转换的长期情况来看，与短期相比，企业在长期的进口市场转换行为更为普遍，进口市场转换率更高，进口市场转换方式更为激进，对国家总进口的贡献也更大。⑤从转换方向和转换模式来看，双向转换是进口企业转换进口市场的主要方向，垂直转换是进口企业转换进口市场的主要模式，双向-垂直转换企业是进口企业进口的核心力量。

（2）进口市场转换对中国企业进口稳定的影响

在此部分，本文首先构建了外部不确定性与进口市场转换交互作用的理论模型，并在此基础上，从理论上分析了外部不确定性增加情形下进口市场转换维持企业进口稳定的渠道；其次，采用2000-2013年中国工业企业数据库、中国海关贸易数据库和WUI数据库的合并数据，实证检验了进口市场转换在平抑外部不确定性对企业进口规模负效应中的作用；最后，进一步考察了进口市场转换方向和进口市场转换路径影响效应的差异性，并基于应对汇率波动的视角再次考察了进口市场转换在稳定企业进口中的重要作用。

研究结果发现：①外部不确定性程度提升会显著抑制中国企业的进口规模，但是，企业通过转换进口市场可以显著平抑外部不确定性对企业进口规模的负效应，有利于企业进口稳定，该结论在进行内生性处理以及稳健性检验之后依旧成立。②从影响机制来看，企业转换进口市场主要通过稳定外部供给、降低进口关税和提升实际有效汇率等渠道平抑外部不确定性对企业进口规模的负效应。③拓展性分析表明，从进口市场转换方向来看，与单纯淘汰进口市场的企业相比，同时新增和淘汰市场的企业、单纯新增进口市场的企业能够更有效地抑制外部不确定性对企业进口规模的负效应；从进口市场转换路径来看，外部不确定性对风险厌恶型企业的进口规模有显著的负效应，但是，对风险偏好型企业的进口规模却有显著的正效应，按照不同的方法对企业类型进行分类，这个结论都是成立的；从应对汇率波动风险来看，转换进口市场也能够显著抑制汇率波动对企业进口稳定的负效应，企业转换进口市场主要通过进口来源地的供给波动和进口市场之间的关联性两个机制发挥作用。

（3）中间品进口市场转换对中国企业出口韧性的影响

在此部分，本文首先从理论上分析了中间品进口市场转换影响企业-目的地出口韧性的机制；其次，使用2000-2016年中国海关贸易数据库数据，实证分析了中间品进口市场转换对企业-目的地出口韧性的影响；最后，进一步考察了中间品进口市场转换对企业在目的地风险抵御能力和出口恢复能力的影响，中间品进口市场转换模式在中间品进口市场转换影响出口韧性中的调节作用，以及中间品进口市场转换对企业在目的地出口波动的影响。

研究结果发现：①企业的中间品进口市场转换行为能够显著增强企业在出口目的地的出口韧性，该结论在进行内生性处理以及稳健性检验之后依旧成立。②从影响机制来看，中间品进口市场转换主要通过分散企业进口中间品的外部风险、扩大企业进口中间品的技术溢出两条渠道增强企业在目的地的出口韧性，不能通过降低中间品进口价格、实现成本节约渠道增强企业在目的地的出口韧性。③中间品进口市场转换对企业-目的地出口韧性的影响会因中间品进口市场转换类型、出口竞争策略、企业规模和目的地受金融危机冲击程度呈现出异质性。④从拓展性分析来看，企业的中间品进口市场转换行为不能显著增强企业在出口目的地的风险抵御能力，却能显著提升企业在出口目的地的出口恢复能力，具体表现为，不仅能够显著缩短企业在出口目的地的出口规模从冲击到企稳所用的时间，而且，也能够显著缩短企业在出口目的地的出口规模从企稳到恢复所用时间；中间品进口市场转换行为对企业在目的地出口韧性的影响并不会因为中间品进口市场转换模式的不同而有所差异；企业的中间品进口市场转换行为还能够显著抑制企业在目的地的出口波动，有利于实现企业在出口目的地的出口稳定。

（4）进口市场转换对中国企业创新的影响

在此部分，本文首先从理论上分析了进口市场转换方向影响企业创新水平的渠道；其次，使用2000-2013年中国工业企业数据库、中国海关贸易数据库和中国企业专利数据库的合并数据，实证检验了进口市场转换方向对企业创新的影响效应和机制；再次，考察了进口市场转换模式对企业创新水平和专利申请结构的影响；最后，考虑到企业创新和企业“稳”增长是企业高质量发展的两个重要衡量维度，还进一步考察了进口市场转换对企业产出增长、就业增长的影响效应和机制。

研究结果发现：①从进口市场转换方向来看，双向市场转换对企业创新有显著的促进作用，单向市场转换对企业创新没有显著影响。影响渠道检验表明，进口规模、进口产品种类和进口产品质量是双向市场转换促进企业创新的重要渠道，企业的吸收能力和进口市场数量在进口市场双向转换与企业创新的关系中具有显著的正向调节效应。②从进口市场转换模式来看，与无市场转换行为相比，水平转换行为显著降低了企业创新水平，垂直向上转换行为对企业创新水平没有显著影响，垂直向下转换行为显著提升了企业创新水平。进一步从创新结构来看，与无市场转换行为相比，水平转换显著降低了企业实用新型专利申请量，对其他两类专利申请量没有显著影响，有利于优化企业的申请专利结构；垂直向上转换对三类专利申请量没有显著影响，对企业的申请专利结构也无显著影响；垂直向下转换显著提升了企业整体的创新水平，但是，增加的专利申请量主要是实用新型专利和外观设计专利，从长期来看，垂直向下转换不利于企业申请专利结构的优化。③从实现企业“稳”增长来看，进口市场转换能够显著抑制不确定性对企业产出增长、就业增长的负效应，有利于促进企业的产出增长和就业增长。

（5）政策建议

根据本文的研究结论，结合中国的现实情况，本文提出，我国政府要高度重视“进口市场转换”在维持进口稳定、增强出口韧性以及提升创新水平方面的重要作用，在努力提高进口贸易便利化程度的同时，也要给予进口企业必要的财政补贴和政策支持，以减少企业转换进口市场的资本约束，鼓励企业积极主动转换进口市场。在此基础上，本文从国家层面、企业层面等方面提出了一些具体的政策建议。

At present, the international situation facing China's opening up is undergoing new changes. Century-old changes in the world are intertwined with century-old epidemics, unilateralism and protectionism are on the rise, economic globalization is encountering adverse trends, and the international environment is becoming more complex, grim and uncertain. In this context, Chinese import firms face severe challenges, how to maintain import stability and ensure the development of firms is a major practical problem. The Chinese government attaches great importance to the optimization of the international market layout, proposes to take firms as the main body, innovate and develop ways, expand diversified international markets, and emphasizes that while deeply cultivating traditional markets, we should also constantly expand emerging markets, promote the steady improvement of foreign trade quality and steady economic operation, and achieve higher quality development. The import market switching behavior of firms is an important way to optimize the international market layout. Based on this, this paper focuses on the important phenomenon of "import market switching", conducts in-depth research on the behavior and function of Chinese firms' import market switching. On the basis of constructing the analysis framework of import market switching and analyzing the stylized facts of import market switching, this paper studies the role of import market switching of Chinese firms from import dimension, export dimension and innovation dimension, and tries to explore a new path for Chinese import firms to realize high-quality development through self-adjustment.

This paper consists of 7 chapters. Chapter 1 is the introduction. Chapter 2 is a literature review. Chapter 3 is the analysis framework and characteristic facts of import market switching. On the basis of constructing the analysis framework of import market switching, it describes the stylized facts of import market switching of Chinese firms from multiple perspectives. Chapter 4 discusses the influence of import market switching on the import stability of Chinese firms, and explores the effect and channels of import market switching to maintain import stability under the circumstance of increasing external uncertainty. Chapter 5 focuses on the impact of import market switching of intermediate goods on export resilience of Chinese firms, and examines the effect and mechanism of import market switching of intermediate goods on firm-destination export resilience. Chapter 6 is about the influence of import market switching on the innovation of Chinese firms, and analyzes the influence of import market switching direction and import market switching mode on the innovation of firms. Chapter 7 is the research conclusion and policy recommendations.

The main research contents and conclusions of this paper are as follows:

(1) Stylized facts of import market switching by Chinese firms

In this part, this paper firstly constructs the analysis framework of import market switching, defines the meaning of import market switching, breaks down the contribution of import market switching to the amount of imports, constructs the switching rate of import market, and further defines the switching path, direction and mode of import market switching. Secondly, it describes the stylized facts of import market switching of Chinese firms from many angles.

Part of the statistical analysis results are as follows: ① Multi-market import firms are the dominant force of Chinese firms' imports. The average data over the years shows that multi-market import firms account for 58.72% of the total number of import firms and 96.30% of the total number of imports. ② The behavior of import firms to switch import market is widespread, and import market switching firms are the leading force of Chinese imports. The behavior of multi-market import firms to switch import market is more prominent. The average data over the past years shows that about 76.29% of all import firms switch import market, and the amount of import accounts for 96.30%. About 92.43% of the multi-market import firms switch import market, accounting for 97.97% of the import value. ③ From the perspective of import market switching rate, the import market switching rate of multi-market import firms is significantly higher than that of all import firms. The statistical results of the average over the years show that the import market switching rate of all import firms is 0.56, and that of multi-market import firms is 0.61. ④ From the long-term situation of the import market switching, compared with the short term, in the long-term firms’ import market switching behavior is more common, the import market switching rate is higher, the import market switching mode is more radical, the contribution to the country's total imports is also greater. ⑤ From the perspective of switching direction and switching mode, two-way switching is the main direction of import firms to switch the import market, vertical switching is the main mode of import firms to switch the import market, two-way-vertical switching firms are the core strength of import firms.

(2) The influence of import market switching on the import stability of Chinese firms

In this part, this paper firstly constructs a theoretical model of the interaction between external uncertainty and import market switching, and then theoretically analyzes the channels of import market switching to maintain import stability under the circumstance of increasing external uncertainty. Secondly, the combined data of China Industrial Firm Database, China Customs Trade Database and WUI database from 2000 to 2013 are used to empirically test the role of import market switching in calming the negative effect of external uncertainties on the import scale of firms. Finally, the paper further investigates the difference of import market switching direction and import market switching path, and again examines the important role of import market switching in the stability of firms' imports from the perspective of coping with exchange rate fluctuations.

The results show that: ① The increasing degree of external uncertainty will significantly inhibit the import scale of Chinese firms, but the negative effect of external uncertainty on the import scale of Chinese firms can be significantly suppressed by switching the import market, which is conducive to the stability of imports of firms. This conclusion is still valid after the endogeneity processing and robustness test. ② From the perspective of influence mechanism, firms' import market switching mainly reduces the negative effect of external uncertainty on firms' import scale by stabilizing external supply, reducing import tariff and increasing real effective exchange rate and other channels. ③ Extended analysis shows that, from the perspective of import market switching, compared with firms that simply eliminate import markets, firms that simultaneously add and eliminate markets and firms that simply add import markets can more effectively inhibit the negative effect of external uncertainty on the import scale of firms. From the perspective of import market switching path, external uncertainty has a significant negative effect on the import scale of risk-averse firms, but it has a significant positive effect on the import scale of risk-taking firms. This conclusion is valid to classify firm types according to different methods. From the perspective of dealing with the risk of exchange rate fluctuations, the switching of import markets can also significantly restrain the negative effect of exchange rate fluctuations on the import stability of firms. Firms' switching of import markets mainly plays a role through two mechanisms: supply fluctuations of import sources and the correlation between import markets.

(3) The impact of import market switching of intermediate goods on the export resilience of Chinese firms

In this part, this paper firstly theoretically analyzes the mechanism of the effect of the import market switching of intermediate goods on the firm-destination export resilience. Secondly, using the data of China Customs trade database from 2000 to 2016, this paper empirically analyzes the impact of import market switching of intermediate goods on firm-destination export resilience. Finally, we further investigate the impact of import market switching of intermediate goods on the risk resilience and export resilience of firms at destination, the moderating effect of import market switching mode between intermediate goods import market switching and export resilience, and the impact of import market switching of intermediate goods on export volatility of firms at destination.

The results show that: ① The import market switching behavior of intermediate goods can significantly enhance the export resilience of firms in export destinations. This conclusion is still valid after the endogeneity treatment and robustness test. ② From the perspective of influence mechanism, the export resilience of firms at destination can be enhanced by diversifying the external risks of firms importing intermediate goods and expanding the technological spillover of firms importing intermediate goods. It cannot be enhanced by reducing the import price of intermediate goods and realizing cost saving. ③ The impact of import market switching of intermediate goods on firm-destination export resilience is heterogeneous due to import market switching type, export competitive strategy, firm size and the impact of financial crisis on destination. ④ From the perspective of extended analysis, the firm import market switching behavior of intermediate goods cannot significantly enhance the firm's risk resistance ability in export destinations, but can significantly improve the firm's export recovery ability in export destinations. Specifically, it can not only significantly shorten the time from the impact to the stabilization of the firm's export scale in export destinations, but also, it can also significantly shorten the time from stabilization to recovery of the export scale of firms in export destinations; The impact of import market switching of intermediate goods on export resilience at destination does not vary with different import market switching modes of intermediate goods. The import market switching behavior of intermediate goods can also significantly restrain the export fluctuation of firms in the destination, which is conducive to the realization of export stability of firms in the destination.

(4) The impact of import market switching on the innovation of Chinese firms

In this part, this paper firstly theoretically analyzes the channels of import market switching that affect the innovation level of firms. Secondly, the combined data of China Industrial Firm Database, China Customs Trade database and China Firm patent database from 2000 to 2013 are used to empirically test the effect and mechanism of import market switching on firm innovation. Thirdly, the influence of import market switching mode on the innovation level and patent application structure is investigated. Finally, considering that firm innovation and "stable" growth are two important measurement dimensions of high-quality development of firms, we further investigate the effect and mechanism of import market switching on firm output growth and employment growth.

The results show that: ① From the perspective of import market switching direction, two-way market switching has a significant promoting effect on firm innovation, while one-way market switching has no significant effect on firm innovation. The influence channel test shows that import scale, import product type and import product quality are important channels for two-way market switching to promote firm innovation, and firm absorption capacity and import market number have a significant positive moderating effect on the relationship between two-way market switching and firm innovation. ② From the perspective of import market switching mode, compared with no market switching behavior, horizontal switching behavior significantly reduces the level of firm innovation, vertical upward switching behavior has no significant impact on the level of firm innovation, vertical downward switching behavior significantly improves the level of firm innovation. Further from the perspective of innovation structure, compared with no market switching behavior, horizontal switching significantly reduces the number of utility model patent applications, but has no significant effect on the number of other two types of patent applications, which is beneficial to optimize the patent application structure of firms. The vertical upward switching has no significant effect on the number of three types of patent applications and the patent application structure of firms. Vertical downward switching significantly improves the overall innovation level of firms, but the increase in patent applications is mainly for utility model patents and design patents. In the long run, vertical downward switching is not conducive to the optimization of patent application structure of firms. ③ From the perspective of achieving "stable" growth of firms, import market switching can significantly restrain the negative effect of uncertainty on firm output growth and employment growth, which is conducive to promoting firm output growth and employment growth.

(5) Policy suggestions

According to the research conclusion of this paper, combined with the reality of China, this paper proposes that the government should attach great importance to the important role of "import market switching" in maintaining import stability, enhancing export resilience and improving innovation level. While making efforts to improve import trade facilitation, the government should also provide necessary financial subsidies and policy support to import firms, so as to reduce capital constraints for firms to switch to import markets and encourage them to actively switch to import markets. On this basis, this paper puts forward some specific policy suggestions from the aspects of national level and firm level.