Abstract: This paper analyzes data from A-share listed manufacturing enterprises from 2010 to 2020 to explore the impact of environmental regulation on the green transformation of these enterprises. The study first examines the direct effects of environmental regulation, then investigates the threshold effect of R&D investment on green transformation, and finally analyzes the mediating role of environmental regulation through technological innovation. The findings indicate that the impact of environmental regulations on the green transformation of manufacturing enterprises follows a U-shaped pattern, where regulations initially hinder and subsequently promote green transformation. This conclusion remains robust after various robustness tests. The threshold analysis reveals that as R&D investment increases, the influence of environmental regulation on green transformation initially suppresses and then enhances these efforts. The mediation analysis demonstrates that environmental regulation facilitates the green transformation of manufacturing enterprises primarily through technological innovation. Furthermore, a heterogeneity analysis reveals that this U-shaped dynamic is consistent across both state-owned and non-state-owned enterprises, as well as in different geographical regions such as the eastern, central, and western parts of the country, although the intensity of regulation varies. Based on these findings, the paper recommends the implementation of differentiated policies tailored to the specific characteristics of enterprises and their regional contexts to boost R&D investment and promote the green transformation of manufacturing enterprises.