Drawing on institutional theory, this paper innovatively develops national-level ESG regulatory variables and employs a threshold panel model to empirically examine the synergistic mechanism through which corporate ESG performance and host-country institutional environments affect MNEs’ international performance. The findings indicate that the positive impact of ESG performance on internationalization performance exhibits a significant institutional threshold effect. The degree of synergistic alignment between the ESG performance of multinational enterprises in their home countries and the ESG regulatory stringency of the host countries jointly determines whether enterprises can effectively convert ESG performance into competitive advantages, thereby enhancing their internationalization performance. Heterogeneity analysis demonstrate that while most ESG dimensions positively impact international performance, the corporate social responsibility dimension shows insignificant effects on overseas subsidiary performance; non-state-owned enterprises and firms in non-high-pollution industries display a stronger positive relationship between ESG performance and international outcomes ; ESG advantages translate more effectively into performance improvements in countries with a surplus of formal ESG institutions and in host countries of the Belt and Road Initiative.