Abstract: Green innovation is an important driving force to promote the green and high-quality development of urban economy. Taking the “Broadband China” demonstration policy as a quasi-natural experiment for information infrastructure construction, based on panel data of 108 prefecture-level cities in the Yangtze River Economic Belt, this paper systematically investigates the direct, indirect and spatial effects of the “Broadband China” demonstration policy on urban green innovation using the staggered difference-in-difference model and the spatial difference-in-difference model. The study finds that information infrastructure construction significantly improves the level of green innovation in cities, and the results remain robust after a series of tests including heterogeneity treatment effects. This improvement effect is more obvious in cities in the lower reaches of the Yangtze River Economic Belt, key cities, and cities rich in scientific and educational resources. The mechanism test shows that information infrastructure construction improves the green innovation level of cities through the talent clustering effect, the Internet level improvement effect, and the digital finance promotion effect. The spatial double difference results show that information infrastructure construction has a spatial spillover effect on urban green innovation, and the policy effect is simultaneously influenced by the economic similarity and geographical proximity of cities. The findings of the study provide empirical insights for further promoting the development of information infrastructure to strengthen urban green innovation.