Voluntary corporate environmental regulation can yield significant environmental and economic benefits, yet how to effectively promote such voluntary actions remains an important question to explore. Using data from China's A-share listed companies participating in the ISO 14001 environmental management certification system from 2010 to 2020, this study empirically examines whether mandatory regulation drives corporate voluntary environmental regulation. The findings indicate that current mandatory regulations in China do not exhibit a significant driving effect on firms' participation in voluntary environmental programs. Further analysis reveals that the primary reasons for this limited impact are insufficient compliance pressure and incentives during the corporate green development process, high costs of voluntary standard implementation, and uncertainties inherent in the certification process. To better encourage voluntary corporate environmental regulation and facilitate the modernization of the environmental governance system, policymakers should further optimize the top-level design of mandatory regulations, strengthen process oversight and environmental information disclosure, foster a supportive external environment for green development, and tighten the supervision of certification agencies.