Based on the panel data of 267 cities in China from 2009 to 2023, this paper empirically examines the impact and mechanism of network infrastructure construction on green technology innovation in cities from both quantitative and qualitative perspectives in accordance with the quasi-natural experiment of “Broadband China” policy by multi-time DID model. The results show that: （1） network infrastructure construction significantly promotes urban green technological innovation in terms of “quantity and quality”. （2） Network infrastructure construction will promote the “quantity and quality”of urban green technological innovation through the mechanism of productive service industry agglomeration and financial development, and the mechanism of industrial structure upgrading can improve the “quantity” of urban green technological innovation, but has no effect on the “quality” of urban green technological innovation. （3） The construction of network infrastructure will differently promote the “quantitative and qualitative” of green technological innovation in cities within different urban agglomerations, and more significantly promote the “quantitative and qualitative” of green technological innovation in cities with a high degree of market development. On this basis, relevant government departments should expand the list of pilots, upgrade the construction program, play a supporting role in the agglomeration of productive service industries, industrial structure upgrading and financial development, plan the network infrastructure construction program according to the situation, narrow the gap about the development of regional green technological innovation, and promote the quality and quantity of green technological innovation by taking the digital transformation as an opportunity.