Chinese society emphasizes connections and circles,and therefore enterprises obtain scarce resources through social capital,an important informal system,which has become a mainstream situation for enterprises to seek development.Based on the integration of the social capital theory into the research on corporate investment behavior,this paper constructed a set of social capital measurement system with two dimensions which include 6 subindicators for social relations and social experience to have comprehensively measured the social capital of top management team (TMT),at the same time,the relationship between social capital of TMT and corporate investment efficiency has been examined too.The result shows that the social capital of TMT has a significant increasing effect on the investment efficiency of the enterprises,and the social capital has more significant influence on the investment efficiency in the area where the legal supervision environment is not perfected.This study verifies the importance of social capital as an informal system in the process of corporate development,and the government should promote the construction of the legal system environment as a formal system to create a fair and good market environment for the development of the enterprises.