This study empirically examines the impact of corporate ESG performance on debt financing costs using a sample of non-financial listed companies on China’s A-share market from 2009 to 2024, with a particular focus on the moderating effect of the 2012 Green Credit Guidelines implementation. The findings reveal: (1) Strong ESG performance significantly reduces corporate debt financing costs, a conclusion that remains robust after a series of stability tests and addressing endogeneity issues. (2) Green credit policies mitigate the debt cost-saving effect of ESG performance. (3) Heterogeneity analysis indicates that this policy moderation effect is more pronounced among non-state-owned enterprises and companies in western China. This study not only provides direct financial incentive evidence for companies to actively pursue ESG strategies but also offers decision-making references for regulators to further refine green finance policy frameworks and implement differentiated guidance.