Abstract: Under the guidance of the strategic objective of "carbon emission peak and carbon neutrality", green innovation has become the key for heavy polluting enterprises to achieve high-quality development. As a mean of market-driven environmental regulation, environmental subsidies provide economic basis and material guarantee for corporate green innovation. However, in reality, local governments have discretion in choosing the objects of subsidies, which is related to both the supporting effect of environmental subsidies and the resource allocation of the national green development strategy. In addition, enterprises can freely choose whether to use environmental subsidies for direct environmental pollution control or green technology research and development innovation. Among them, there are problems to be further explored: in which kind of firms are the supporting effect of environmental subsidies on corporate green innovation better? Based on Porter's hypothesis, stakeholder theory and institutional theory, the panel threshold regression model was adopted to examine and validate the differential impact of environmental protection subsidies on corporate green innovation as well as the internal mechanism among 337 listed companies operating in heavily polluting industries over the period spanning from 2010 to 2019. The results show that: (1) The incentive effect of environmental protection subsidies on corporate green innovation is mainly effective for firms that cross the threshold of corporate social responsibility. Firms with high CSR level have green development consciousness and need to upgrade their products and technologies through green innovation; On the other hand, firms with high CSR level have abundant external resources, such as green resource integration and talent introduction, while environmental subsidies ease the financial pressure and resource constraints within firms, providing favorable conditions for firms to make better use of environmental subsidies for green innovation. (2) When the firms cross the threshold of CSR, the incentive effect of environmental protection subsidy on corporate green innovation is better in state-owned enterprises. The status of state-owned firms can escort the incentive mechanism of environmental subsidies for green innovation, which can better play the role of environmental subsidies in promoting corporate green innovation. This paper contributes to the literature from the four perspectives. Firstly, this paper extends the theoretical extension of Porter's hypothesis. The traditional Porter hypothesis focuses on the influence of environmental regulation policy mix and optimal interval on enterprises' green innovation. On this basis, this paper expands the hypothesis to the perspective of stakeholder status and institutional foundation to explore the micro-mechanism of environmental subsidies affecting enterprises' green innovation mechanism. Secondly, according to the stakeholder theory, it is proposed that there is a threshold of CSR in the process of promoting enterprise green innovation with environmental protection subsidies. The level of CSR means the resource guarantee, attention pressure and innovation coordination from stakeholders, which expands the theoretical connotation of stakeholder theory in the field of green innovation. Thirdly, based on the institutional theory, this paper proposes that the state-owned firm identity will promote the mechanism of green innovation driven by environmental protection subsidies after CSR crosses the minimum threshold, enriching the research perspective of institutional theory and extending it to the research on the related mechanism of the anthems of green innovation. Finally, based on threshold effect, this paper constructs the micro-mechanism of environmental protection subsidies driving corporate green innovation with threshold of CSR. Previous studies focus on the optimal interval of environmental regulation intensity based on Porter's hypothesis. This paper endeavors to investigate the threshold mechanism and expand the research on the micro-mechanism of the antecedent variables that lead to corporate green innovation.