本文以2009年至2021年中国A股上市公司为样本，研究了社保基金持股对企业ESG表现的正向影响作用，既检验了社保基金持股的部分传导机制，也检验了不同机构投资者之间的异质性，以及产权性质、企业规模、地域市场化程度等因素对社保基金持股与企业ESG水平关系之间的调节作用。研究发现：（1）社保基金持股能显著提高企业的ESG表现，这种改善效果会随社保基金持股比例的提升而提升，会随时间的推移而减弱，同时持股比例对企业ESG改善作用随持股比例的提升呈边际效用递减。（2）社保基金是否持股本身，比持股比例的大小对企业ESG表现的改善作用更强。（3）对比社保基金通过外部管理人主动持股行为和国有资产划转的被动持股行为，社保基金主动持股的上市公司ESG改善作用更为显著。本文分析了这种改善作用的部分传导路径：（1）社保基金的外部管理人作为股东方施加影响，通过降低企业经营中潜在负面风险因素，提升ESG水平。（2）社保基金通过引起分析师对被持股企业的关注，对企业施加压力来发挥作用。（3）社保基金管理人和分析师与被投企业的互动提升了企业的透明度，使得企业暴露在更广泛的社会监督之下，面临更大的社会压力，而主动使行为符合社会预期。进一步分析社保基金作为机构投资者的异质性特征发现：（1）在国内不同类型的机构投资者中，社保基金对企业ESG治理改善作用最为明显。（2）产权性质、企业规模、市场化程度、产业类型对社保基金持股与企业ESG水平之间的关系有调节作用。社保基金对非国有企业、大市值企业、市场化程度高区域的企业，以及高新产业企业的ESG水平改善作用更为突出。拓展分析发现，社保基金对企业ESG水平中的环境因素（E）的改善作用最明显，再次说明了社保基金的绿色金融价值。本研究为全面理解社保基金权益投资行为对企业ESG治理的影响作用提供了参考，亦为研究该影响作用的传导机制提供了部分思路，也为国家制定政策来促进机构投资者积极发挥绿色金融价值，提升企业ESG水平，落实国家绿色发展政策提供了相应依据。

This paper examines the impact of SSF’s ownership on enterprise’s ESG performance through examining China's A-share listed companies from 2009 to 2021. The study found that SSF’s ownership significantly improved enterprises’ ESG performance with the increase of the shareholding but decreases the marginal effect. For the ESG improvement, SSF’s ownership means more than the holding ratio and the effect only works profoundly in the actively invested companies. This paper also analyzes some of the transmission paths of this improvement and found that internal control, analysts’attention and disclosure report played vital roles for the mechanism. Further analysis of the heterogeneity of SSF not only revealed its superior effect on enterprises’ ESG performance improvement comparing to other institutional investor, it also unfolded that the nature of property right, size, marketization and industry attributes have moderating effect on the relationship between SSF’s ownership and the level of enterprise ESG performance. When separating ESG into environment(E), social(S) and governance(G), SSF’s ownership connected more with environmental concerns which high lights on the green financial value of SSF. This study provides a reference for a comprehensive understanding of the impact of SSF’s equity investment on enterprises’ ESG performance. It also provides a corresponding basis for the government to formulate policies by promoting institutional investors’ active ownership in raising companies’ ESG performance.