To explore whether pilot policies for social credit system reform can improve corporate ESG performance while achieving the goal of creating a favorable business environment. The study takes the implementation of pilot policies for social credit system reform as a "quasi natural experiment", based on strategic social responsibility theory, social capital theory, and agency theory, using A-share listed companies from 2009 to 2023 as samples, to explore and verify the impact and internal mechanism of social credit system construction on corporate ESG performance. Research has found that the construction of a social credit system can improve the ESG performance of enterprises in pilot areas; Mechanism analysis shows that the construction of a social credit system can improve corporate ESG performance by increasing social capital and reducing agency costs; Institutional investors' shareholding has a positive moderating effect on the relationship between social credit system construction and corporate ESG performance, and the moderating effect of institutional investors' shareholding shows significant heterogeneity. Pressure resistant institutional investors' shareholding positively moderates the impact of social credit system construction on corporate ESG performance, but the moderating effect of pressure-sensitive institutional investors' shareholding is not significant. Further analysis shows that the effects of the pilot program are stronger in enterprises with state-owned property rights, lower internal governance levels, secondary industries, and better business environment in their respective regions. In addition, the construction of a social credit system can help alleviate ESG uncertainty and improve the quality of corporate ESG information. The pilot reform of the social credit system has brought about an improvement in the ESG performance of enterprises, which can also alleviate financing constraints and promote high-quality development of enterprises. The study provides micro evidence for promoting corporate ESG performance in the construction of a social credit system, which helps to further deepen the construction of the social credit system and achieve coordinated development of the economy, society, and environment.