Abstract: The paper takes the cross-border mergers and acquisitions of domestic listed companies from 2011 to 2023 and studies the causal effect between cross-border mergers and acquisitions and corporate ESG performance. Cross border mergers and acquisitions significantly improve the ESG performance of the acquiring company. From the perspective of cross-border merger and acquisition types, both horizontal and vertical cross-border mergers and acquisitions can have a significant positive impact on the ESG performance of the acquiring company, and the impact of horizontal cross-border mergers and acquisitions is stronger; Mechanism analysis shows that cross-border mergers and acquisitions mainly exert spillover effects and reputation effects, which indirectly affect the ESG performance of enterprises. The former helps enterprises carry out internal green innovation, while the latter helps enterprises gain external media attention. Based on this, corresponding countermeasures and suggestions are proposed from the aspects of recognizing the positive effects of cross-border mergers and acquisitions, strengthening spillover effects and reputation effects.