In recent years, driven by China’s carbon peaking and carbon neutrality targets, the regulatory framework for semi-mandatory environmental information disclosure has become more complete, and ESG report publication has expanded rapidly. Drawing on information asymmetry and related theories, this study investigates how ESG performance influences corporate financing costs. Using a sample of 1,044 A-share listed companies from 2016 to 2020, the paper compiles and analyzes ESG disclosure and rating data to construct firm-level ESG performance indicators, and then develops an empirical model to test the relationship between ESG performance and financing costs. The analysis further examines whether this relationship varies across different types of firms, and evaluates the moderating roles of firm size and media attention in shaping the ESG–financing cost linkage. The results indicate that firm size plays a positive moderating role in the effect of ESG performance on financing costs.