The recent occurrence of global extreme climate events has prompted the international community to pay more attention to environmental issues. Characterized by high emissions and high pollution, thermal power enterprises have entered a critical period of transition towards clean energy. In response to the increasingly serious environmental pollution problem, the China government has begun to levy environmental protection taxes nationwide. This research selects 21 listed thermal power enterprises in China as the sample and uses a three-stage (operation, green transformation, and market performance) DEA evaluation model to evaluate the efficiency of their green transformation and corporate performance. We integrate comprehensive indicators such as ESG (environment, social, governance), stock price, and energy substitution returns into the model and conduct comparative research based on the macro-level policies and geographical location of the enterprises’ location. Using environmental tax burden as an exogenous variable, comparative analysis is conducted on corporate efficiency before and after adjusting the environmental tax burden. In terms of overall efficiency, there is a certain positive correlation between the overall efficiency value of thermal power enterprises and the economic development of the region in which they are located. In terms of stage efficiency, the green transformation efficiency of most thermal power enterprises is superior to market performance efficiency. In terms of sub-indicator efficiency, the efficiency values of input-output indicators in various stages of thermal power enterprises are mostly in a stable and progressive state. The environmental tax burden mainly improves the overall efficiency of thermal power enterprises by raising operational efficiency and green transformation stage efficiency, without affecting market performance efficiency. To further increase efficiency, thermal power enterprises should actively establish communication channels with stakeholders and alleviate financial difficulties caused by green transformation as much as possible. In addition to continuing to implement environmental tax collection, government departments should also designate a series of targeted subsidy policies.
