The carbon emissions trading policy is a key policy driving China’s low-carbon economic transition. Based on the policy environment of China’s carbon emissions trading pilot program from 2010 to 2021, this research selects representative heavy-polluting listed enterprises from this period as research subjects. Using the DID model, it investigates the impact of the carbon emissions trading policy on corporate ESG performance. The results of the research show that: (1) The carbon emissions trading policy significantly improves the ESG performance of heavy-polluting enterprises. (2) The carbon emissions trading policy enhances corporate ESG performance primarily by alleviating external financing constraints and stimulating green technological innovation within enterprises. (3) Due to differences in corporate characteristics and decision-making structures, the impact of carbon emissions trading policies on the ESG performance of heavily polluting enterprises exhibits heterogeneity. The findings of research are of great significance for a comprehensive understanding of the carbon emissions trading policy, facilitating fundamental changes in enterprises, promoting the construction of the carbon emissions trading market, and ensuring the timely achievement of the “dual carbon” goals.