根据金融深化理论和金融抑制理论，发展中国家对于金融市场的过度干预会影响市场的均衡状态，进而影响经济发展，故应当放开相关管制，由市场进行调节。于是我国不断推进利率市场化，于1993年提出利率市场化的初步构想，1996年正式推进，到2015年基本完成，整个过程历时二十多年。在此期间有许多学者对利率市场化会带来怎样的影响进行了研究，本文将从商业信用和投资效率的角度出发进行研究，研究利率市场化对投资效率的作用以及商业信用在两者关系中扮演怎样的角色。 商业信用是企业十分重要的一项负债，是日常经营中必不可少的资源，许多企业利用自身的优势地位实施OPM（Other People’s Money）战略。这些企业在采购原材料时没有立即付款，占用供应商的资金，但在销售时收取现款确保了自身资金的回收，这种方式增加了企业的可运用资金量。本文试图探究利率市场化之后企业对商业信用的使用是否发生改变，而商业信用的使用是否会影响企业的投资效率，即商业信用在利率市场化和投资效率之间是否发挥中介效应，从一个较新的角度看待商业信用的作用。 我国目前已基本完成了利率市场化进程，提供了从完整发展历程分析利率市场化作用的环境，在这个背景下本文针对利率市场化、商业信用与投资效率的关系展开研究，以利率市场化专家打分指标和利率市场化贡献赋值指标两个指数来衡量利率市场化进程，选择2003年—2017年沪深A股非金融上市公司作为研究样本，构建模型衡量利率市场化对商业信用的影响，利率市场化对投资效率的影响，以及商业信用的中介效应。本文的实证结果显示，利率市场化能够提高企业投资效率、提高企业对商业信用的使用，并验证了商业信用的中介作用，即利率市场化能够通过商业信用影响投资效率，进行了稳健性检验后结论并未发生改变。 本文采用指数方式衡量利率市场化，相比以往简单采取虚拟变量方式衡量利率市场化的文章，能够从一个更完整的角度来看待利率市场化的作用，同时本文将商业信用作为中介变量较有新意，能够对利率市场化、商业信用和投资效率的相关研究有所补充。

According to the financial deepening theory and financial repression theory, the excessive intervention of developing countries in the financial market will affect the equilibrium state of the market and thus affect the economic development. Therefore, relevant regulations should be liberalized and regulated by the market. China put forward the preliminary idea of interest rate liberalization in 1993, formally promoted it in 1996, and basically completed it in 2015. The whole process took more than 20 years. Many scholars have studied the impact of interest rate liberalization. Trade credit of the enterprise is a very important kind of liability, and is an essential resource in the enterprise daily management. Many enterprises rely on their market positions to carry out the strategy of OPM (Other People’s Money): procure raw materials without immediate payment, taking up the suppliers of capital, but collect money right away when sale the products, ensuring the recovery of their own capital. In this way, enterprise can increase the overall amount of capital available. This paper attempts to explore whether the use trade credit by enterprises changes after interest rate liberalization, and whether the utilization of trade credit will affect the investment efficiency of enterprises, that is, whether trade credit plays an intermediary role between interest rate liberalization and investment efficiency. Now China has basically completed the market-oriented interest rate process, which provides a favorable condition to study the role of interest rate liberalization. Given the complete development process, this paper researches on the relationship with trade credit and investment efficiency, taking two index- expert grading index and interest rate marketization of interest rate liberalization contribution assignment - to measure the interest rate marketization process, and selecting 2003-2017 Shanghai and Shenzhen A-share non-financial listed companies as research samples. The model is built in the article to measure the effect of interest rate marketization on trade credit and investment efficiency, and the mediation effect of the trade credit. The result turns out that the marketization of interest rate can improve the efficiency of corporate investment, improve the use of trade credit; whilst trade credit can enhance the efficiency of investment, which verifise the mediating role of trade credit. In another words, the interest rate marketization can affect investment efficiency through trade credit. The conclusion still can be hold after robustness test. Compared with past researches that simply use virtual variable to measure interest rate marketization, this article analyzes the role of interest rate marketization more thoroughly by adopting the index method. At the same time, it is creative to set trade credit as the intermediary variable. This article can serve as a valuable supplementary to the study of relation among interest rate marketization, trade credit and investment efficiency.