<p>Environmental protection tax law (EPTL) is an important policy tool to realize the coordinated development of economy and environment, and the realization degree of its Porter hypothesis effect (PHyE) needs to be evaluated urgently. Drawing upon sample data from state-owned, private, and foreign-invested enterprises, this research conducts empirical testing via a multiple regression framework. Empirical results suggest that the EPTL has yet to achieve the full potential of the Porter hypothesis (PHy), while current implementation modalities partially suppress green innovation activities. This negative effect is most significant in private enterprises. To better stimulate the PHyE of EPTL and promote green technology innovation (GTI), the tax law implementation modalities should be optimized from the aspects of strengthen the environmental and tax authorities' communication and coordination, private enterprises shall be severely punished for speculation in automatic monitoring, strengthen the training of private enterprises in tax return business and improve their tax return capability, and enhance the effectiveness and accuracy of information disclosure in the management and enforcement of EPT. This study extends the analytical lens on tax law implementation, underscoring the imperative to tailor environmental policy instruments to enterprises' distinct ownership structures for enhanced innovation stimulation. It thereby offers theoretical and practical contributions to future environmental regulation and PHy scholarship.</p>