技术与人类的生产生活息息相关，技术的每一次变革与进步，都深刻地影响着人类的生产方式，改变工作内容，改造职业形态。第三次工业革命以来，尤其是进入20世纪九十年代后，以计算机技术为代表的信息技术（ICT）在工作中得到大规模的应用，这使得大量过去由人从事的工作，特别是那些可以被计算机编程控制的重复性和指令性工作，逐步被计算机所替代。与此同时，经济全球化和国际贸易也在不断塑造劳动力市场新的格局，发达国家将一部分制造业等行业的工作岗位外包给发展中国家。在技术进步和全球化共同作用之下，欧美等发达国家的职业结构普遍出现了工作“极化”的现象。

技术进步等因素的作用也同样改变了发展中国家的职业结构，但由于在技术水平、劳动力结构、经济发展水平等诸多方面存在较大差异，发展中国家与国家之间的职业结构变化截然不同。过去四十年来，作为世界上最大的发展中国家和第二大经济体，中国承接了大量的发达国家的生产外包任务，并在技术应用、科技创新、管理理念等多方面，吸收国际先进经验，取得了举世瞩目的经济发展，并使中国的劳动力市场发生了巨大变化。与此同时，中国城镇化进程的推进和以义务教育、大学扩招为代表的教育扩张，普遍性地改善了中国的人力资本状况，极大地促进了中国的劳动力流动，每年数以亿计的劳动力，从农村地区、经济落后地区涌向发展更好的城市和地区。这种国家内部的、跨区域的劳动力流动，特别是“乡-城”流动，对中国职业结构变迁产生了难以估量的影响。对于劳动力流入地城市的职业结构来说，这种影响更难以忽视，甚至重塑了区域劳动力市场。持续的巨大体量的人口流动，也在悄然发生变化，随着教育水平提高、户籍制度改革、人口结构变化、社会观念变迁等等现象，流动人口的居留意愿也出现转变，定居意愿愈发强烈，家庭化迁移的趋势愈发明显。而在这一过程中，不同城市之间、城市本地居民和外来移民之间、具备不同人力资本背景的移民之间，所呈现的特征纷繁复杂，所受到的影响差别迥异，不同家庭对不同区域劳动力市场的选择也不尽相同。

基于上述背景，本文利用1990-2015年人口普查和1%人口抽样调查数据，以及《中国城市统计年鉴》等数据，以工作任务为视角，研究了如下几个方面的问题，具体而言，首先，刻画了技术进步背景下的中国职业结构变迁的特征事实和变化趋势；其次，探讨了低技能劳动力流入对城市低技能劳动力市场职业结构的影响；再次，揭示了城市密度如何影响不同类型的夫妻职业距离；最后，分析了夫妻教育水平如何影响家庭迁移与城市区位选择。本文得到的主要研究结论如下：首先，1990年-2015年，中国的职业结构总体上呈现出就业升级的趋势，表现为低收入水平的职业（如种植业）的大量减少，以购销为代表的其他类型职业的就业份额迅速增加。但是在城市的非农业部门和非政府部门的就业群体中，在不同时期，职业结构呈现出不同的特征：1990-2000年，常规任务类型职业和手工任务类型职业的就业份额下降，抽象任务类型职业的就业份额上升，就业趋势呈现出职业升级现象；2000-2015年，从事常规任务类型职业的份额下降，从事高收入抽象任务类型职业和低收入手工任务类型职业的份额上升，职业结构呈现“U”型极化现象，这种现象在市区的就业群体中更为明显。从城市职业结构变化趋势来看，1990年常规任务指数越大的城市，在2015年城市其从事低技能手工任务类型职业份额增加的比例越高。

其次，低技能跨市外来移民的流入会对城市低技能劳动力市场的职业结构产生影响。跨市外来移民在从事手工任务指数较高的职业类型时具有比较优势，而城市本地居民在从事沟通指数较高的职业类型时具有比较优势，由于两类就业群体在职业类型比较优势的不同，城市劳动力市场的跨市外来移民与本地居民并不是简单的完全替代关系。利用2000-2015年人口普查或1%人口抽样调查数据进行实证研究，本文的研究结果表明：在285个城市中，城市低技能外来移民的比例越高，本地居民从事沟通任务指数较高的职业类型比例越高，该城市的沟通任务与手工任务的相对价格也越高；异质性分析表明，如果低技能跨市外来移民是具有农业户口、女性和高中学历等特征，则上述结论更加显著。

再次，城市人口密度的增加会影响夫妻的职业距离。城市集聚导致人口密度的增加，这会增加城市职业的多样性，夫妻双方根据各自的比较优势，会更容易在城市找到与自身能力匹配的工作岗位。利用2000-2015年人口普查或1%人口抽样调查数据和相应年份的《中国城市统计年鉴》数据，进行实证研究，本文实证研究表明：在285个城市中，城市人口密度每增加1%，夫妻职业距离增加1.049%，这一研究结论对于低学历夫妻类型家庭和跨市外来移民家庭尤为显著。

最后，夫妻双方的受教育水平会影响其家庭迁移决策和城市的区位选择，高学历类型的夫妻家庭由于存在工作地点共同选址的问题，更倾向于迁移，并且迁移目的地更倾向于大中城市。利用2000-2015年人口普查或1%人口抽样调查数据进行实证研究，本文研究结果表明：在285个城市中，如果夫妻双方都具有大专及以上学历，在人户分离迁移模式下，家庭户主进行跨县区迁移的概率将提高5.0%-5.8%，跨县区及以上迁移的概率将提高0.5%-7.3%；对于夫妻双方均为大专及以上学历的家庭，其户主迁移至大中城市的概率是夫妻双方均为高中及以下学历的家庭的0.9-2.7倍；从夫妻双方各自的教育水平来看，丈夫教育水平和妻子教育水平对家庭户主迁移决策和城市区位选择的影响并无显著性差异。

基于以上研究结论，本研究提出如下政策建议：首先，技术进步是非中性的，技术进步与抽象任务类型职业是互补的关系，对手工任务类型职业负面影响较小，但是对常规任务类型职业的负面冲击较大。因此需要对从事常规任务类型职业的劳动力加大相关技能培训，合理引导他们进入抽象任务和手工任务类型职业领域，减轻技术进步对于职业负面影响；其次，由于低技能跨市外来移民和城市本地居民所从事职业类型的差异性，低技能跨市外来移民不仅不会对低技能城市本地居民产生较大替代性，反而能够促进城市本地居民从事收入水平更高的沟通任务类型职业，所以，限制低技能外来移民的流入将损害城市本地居民和跨市外来移民的福利。因此，城市政策制定者要逐步消除各种限制劳动力流动的制度壁垒，取消对于外来低技能劳动力的歧视性政策，促进低技能劳动力的自由有序流动；最后，城市规模的扩大引起人口密度的增加，即城市集聚，这不仅能够增加劳动力市场职业多样性， 提高不同技能劳动力的职业匹配效率，扩大夫妻职业距离，而且还会吸引高学历家庭的夫妻双方，为了更好地匹配各自的工作，迁移到大中城市。因此，城市政策制定者应该适当放宽限制大中城市人口规模的政策，发挥好城市集聚效应，促进不同技能劳动力在城市劳动力市场更好的职业匹配。

The technology is closely related to the production and life of human beings, and every change and progress of the technology deeply influences the production mode of the human, changes the work content, and transforms the professional form. Since the third industrial revolution, especially since the 1990s, the information technology (ICT), represented by computer technology, has been applied in a large scale in its work, which makes a lot of work done by people in the past, In particular those which can be programmed and controlled by computer and are gradually replaced by computer. At the same time, economic globalization and international trade have also shaped a new pattern of the labour market, and developed countries have outsourced jobs such as part of the manufacturing sector to developing countries. Under the common role of technological progress and globalization, the working "polarization" of the professional structure of the developed countries, such as Europe and the United States, have generally occurred.

The role of technological progress and other factors have also changed the professional structure of developing countries, but because of the great difference in the technical level, the labor structure and the level of economic development, the change of the professional structure between the developing countries and the country is very different. Over the past four decades, as the world's largest developing country and the second-largest economy, China has undertaken a large number of production and outsourcing tasks in developed countries, and has absorbed international advanced experience in the fields of technology application, science and technology innovation and management concept. The world-wide economic development has been achieved, and the labor market in China has changed greatly. At the same time, the promotion of the Chinese urbanization process and the education expansion represented by the compulsory education and the expansion of the university have greatly improved the human capital situation in China, greatly promoted the labor movement of China, and Hundreds of millions of labor every year, from rural areas and economically backward areas flock to better developed cities and regions. The internal and cross-regional labor movement, in particular the "Rural-City" flow, has an immeasurable effect on the change of Chinese professional structure. This effect is more difficult to ignore and even remodelling the regional labour market for the professional structure of the labour-to-ground city. The constant mass flow of the population is also quietly changing. With the improvement of the level of education, the reform of the household registration system, the change of the population structure, the change of the social concept and so on, the will of the floating population will change, and the will of the settlement will become stronger. The trend of family migration is becoming more apparent. In this process, among the different cities, between the local residents of the city and the foreign immigrants, the characteristics of the presented characteristics are complex, the influence is different, and the different families have different choices on the labor market of different regions.

Based on the above background, this paper uses the data of the 1990-2015 population census and 1% of the population sample survey data, as well as the data of the Urban Statistical Yearbook of China, to study the problems in the following aspects, in particular, first, The paper describes the characteristics and trends of the change of Chinese professional structure in the background of technological progress, and then discusses the influence of the low-skilled labor force on the professional structure of the low-skilled labor market in the city. Finally, how to influence family migration and city location selection is analyzed. The main findings of this paper are as follows:

First of all, from 1990 to 2015, the occupational structure of China generally showed the trend of employment upgrading, showing a large decrease in low-income occupations (such as planting), and the employment share of other types of occupations represented by purchase and sale increased rapidly. However, in the urban non-agricultural sector and non-governmental sector employment groups, in different periods, the occupational structure presents different characteristics: from 1990 to 2000, the employment share of conventional task type occupation and manual task type occupation decreased, the employment share of abstract task type occupation increased, and the employment trend showed the phenomenon of career upgrading; From 2000 to 2015, the share of conventional task type occupation decreased, the share of high income abstract task type occupation and low income manual task type occupation increased, and the occupation structure showed "U" polarization phenomenon, which was more obvious among the urban employment groups. According to the changing trend of urban occupational structure, the higher the conventional task index in 1990, the higher the proportion of cities engaged in low-skilled manual tasks in 2015.

Second, the inflow of low-skilled immigrants across the city will have an impact on the occupational structure of the urban low-skilled labor market. Inter-city immigrants have comparative advantages when they are engaged in occupational types with higher manual task indexes, while urban local residents have comparative advantages when they are engaged in occupational types with higher communication indexes. Because of the different advantages of occupational types in the two types of employment groups, Inter-city immigrants in the urban labor market are not simply a complete substitute for local residents. Using the 2000-2015 census or 1% population sample survey data for empirical research, the results of this study show that in 285 cities, the higher the proportion of urban low-skilled immigrants, the higher the occupation of local residents in communication tasks, and the higher the relative price of the city's communication tasks and manual tasks; heterogeneity analysis shows that if low-skilled immigrants are characterized by agricultural hukou, women, and high school education, the above conclusions are more significant.

Third, the increase in urban population density will affect the occupational distance of couples. Urban agglomeration leads to an increase in population density, which will increase the diversity of urban occupations. Couples will be more likely to find jobs that match their own abilities in the city according to their respective comparative advantages. Based on the data of 2000-2015 census or 1% population sample survey and the data of China Urban Statistical Yearbook in corresponding years, the empirical study shows that the occupational distance between husband and wife increases by 1.049% for every 1% increase in urban population density in 285 cities, this conclusion is particularly significant for low-education couples and cross-city immigrant families.

Finally, the education level of husband and wife will affect the decision of family migration and the location choice of city. Because of the problem of common location of workplace, couples with high-education type tend to migrate, and the destination of migration is more inclined to large and medium-sized cities. Using the data of 2000-2015 census or 1% population sampling survey, the results show that in 285 cities, if both husband and wife have college education or above, the probability of household head moving across counties and districts will be increased by 5.0% and 5.8%, and the probability of inter-county and above migration will be increased by 0.5% and 7.3%, respectively. For families with college education or above, the probability of the head of household moving to large and medium-sized cities is 0.9 times higher than that of families with high school education and below. From the educational level of both husband and wife, there is no significant difference in the influence of husband's education level and wife's education level on the migration decision-making and urban location choice of the head of household.

Based on the above conclusions, this study puts forward the following policy suggestions: first, technological progress is non-neutral, technological progress and abstract task type occupation are complementary, and have little negative impact on manual task type occupation, but have a great negative impact on conventional task type occupation. Therefore, it is necessary to increase the training of relevant skills for the labor force engaged in conventional task type occupations, reasonably guide them into abstract tasks and manual task type occupations, and reduce the negative impact of technological progress on occupations. Secondly, due to the difference of occupation types between low-skilled cross-market immigrants and urban local residents, low-skilled cross-market immigrants will not only not produce greater substitution for low-skilled urban local residents, but can promote urban local residents to engage in higher income level communication task type occupations. Therefore, restricting the inflow of low-skilled immigrants will harm the welfare of urban local residents and cross-market immigrants. Therefore, urban policymakers should gradually eliminate all kinds of institutional barriers that restrict the movement of labor force, eliminate the discriminatory policies against foreign low-skilled labor force, and promote the free and orderly movement of low-skilled labor force. Finally, the expansion of urban scale leads to the increase of population density, that is, urban agglomeration, which can not only increase the occupational diversity of the labor market, improve the efficiency of career matching of different skilled labor forces, expand the professional distance between husband and wife, but also attract the husband and wife of highly educated families to migrate to large and medium-sized cities in order to better match their respective jobs. Therefore, urban policymakers should appropriately relax the policy of restricting the population size of large and medium-sized cities, give full play to the effect of urban agglomeration, and promote better job matching of different skilled labor in the urban labor market.