In the context of "double carbon", how to improve environmental quality through green technology innovation? What role does the government play in the green transformation of production and lifestyle?Based on the data of 263 prefecture-level and above cities from 2004 to 2018, it used different dimensions to measure environmental quality, and used panel data model to empirically test the relationship between green technology innovation and urban environmental quality under fiscal decentralization. The results show that green technology innovation has a significant improvement effect on urban environmental quality, and there is an interaction between green technology innovation and fiscal decentralization, and the improvement effect of green technology innovation on environmental quality decreases with the increase of fiscal decentralization. The moderating effect of fiscal decentralization on the improvement of environmental quality driven by green technology innovation has regional heterogeneity, time difference and threshold effect. Therefore, it is necessary to control the level of fiscal decentralization according to local conditions, increase investment in urban green technology innovation, improve the utilization rate of green technology, and accelerate the realization of the goal of green and low-carbon development of cities.