This study examines how emerging market multinational enterprises (EMNEs) respond to cross-national diversity in environmental regulation. Prior research suggests that internationalization exposes EMNEs to diverse environmental standards and may facilitate regulatory learning, yet offers a limited understanding of the mechanisms through which such exposure translates into green innovation. Drawing on institutional theory, we argue that green innovation is particularly fostered when EMNEs operate across host countries whose environmental regulatory regimes are more stringent than those in the home country, and when such exposure varies across multiple host locations. We theorize that this form of environmental regulatory diversity creates learning pressures and legitimacy incentives that motivate EMNEs to upgrade their environmental capabilities through green innovation. Using panel data comprising 9,362 firm-year observations from 1,088 Chinese MNEs over the period 2008–2021, we find support for our arguments. We further show that these effects are contingent on organizational and institutional conditions, specifically top management teams’ technological expertise and the strength of intellectual property enforcement in home-country locations. These findings advance research on EMNE learning and sustainable innovation under complex global environmental governance.