Select sample data from A-share listed companies in Shanghai and Shenzhen Stock Exchanges from 2013 to 2021 to study the impact of environmental tax reform on audit fees. Research finds that the environmental tax system can significantly reduce audit fees, and the above conclusion remains valid after a series of robustness tests. Mechanism test shows that the reform of environmental tax system reduces audit fees by exerting the “environmental risk governance effect” and “production structure optimization effect”. Heterogeneity analysis shows that the impact of environmental tax reform on audit fees varies with the characteristics of audit suppliers and demanders, as well as with the macro external environment. The research conclusion not only enriches the research on the policy effects of environmental tax reform at the micro level, but also helps auditors strengthen their risk awareness of environmental tax reform, providing useful reference for promoting high-quality development of the capital market.