This study investigates the impact of the national innovative city policy on enterprise green technology innovation amid China’s transformation from a resource-dependent to an innovation-driven economy. Working on city- and enterprise-level data from 2003 to 2018, this study employs the multi-period difference-in-differences (DID) model and the Sobel test to explore the impact of innovative city policies. The empirical results demonstrate that the innovative city policy has improved both the quantity and quality of enterprises’ green technology innovation output. This positive impact is accomplished via improving the urban innovation environment and stimulating enterprise research and development (R&D) investment. The promoting effect of the policy is stronger in attaining green utility patents by state-owned enterprises and green invention patents by non-state-owned enterprises. The positive policy impact is more pronounced for large enterprises. This study provides micro-level evidence regarding the policy’s impact on green innovation, and the results carry valuable policy implications.