The Impact of the Environmental Tax on the Green Transition of Marine Enterprises: Evidence from China

Against the backdrop of increasing vulnerability of global marine ecosystems, leveraging market-based environmental regulation to promote the green transition of marine enterprises has become a central policy concern. This study utilizes the implementation of China’s Environmental Protection Tax Law (EPTL) in 2018 as a quasi-natural experiment and constructs an intensity-based difference-in-differences (DID) framework using panel data on marine-related firms from 2010 to 2023. The core dependent variable is a firm-level green transition index derived from textual analysis of annual reports, measured as the natural logarithm of one plus the frequency of green-transition-related keywords, capturing firms’ strategic commitment to environmental sustainability. The results show that the EPTL significantly increases the log frequency of green-transition-related keywords in annual reports, indicating that tax-induced cost pressure is translated into firms’ strategic environmental reporting. The findings remain robust to alternative dependent variables are employed, including the share of green invention patents in total patent grants and pollution emission intensity per unit of revenue. Mechanism analysis suggests that the policy operates through strengthened external supervisory pressure and enhanced firm-level innovation incentives. Heterogeneity analysis indicates that the policy effect is more pronounced among firms with core marine businesses, those in the midstream of the industrial chain, firms facing lower financing constraints, and those operating in highly competitive industries. The results remain stable after a series of robustness and endogeneity tests. This study extends the theoretical boundary of environmental taxation in the context of the marine economy, provides micro-level evidence for the effectiveness of market-based environmental instruments in developing countries, and offers policy insights for refining differentiated environmental taxation, strengthening coordinated regulatory systems, and improving green financial support mechanisms.