Abstract: Abstract：Urban decarbonization is a crucial strategy for achieving the "dual-carbon" goal and fostering sustainable development.Concurrently, the integration of financial technology and green finance constitutes a significant approach to advancing urban decarbonization.Based on established mechanism for the synergistic promotion of urban decarbonization by fintech and green finance, this study conducted a research by selecting 108 prefecture-level cities in the Yangtze River Economic Belt from 2010 to 2021.Utilizing a comprehensive application of the coupled coordination model, kernel density estimation, spatial autocorrelation analysis, and econometric model, we empirically analyzed the spatiotemporal evolution characteristics of the synergistic development of fintech and green finance and examined the mechanism of the impact on urban decarbonization.The results showed that: (1) The synergistic evolution of fintech and green finance within the study area progressed from minimal to moderate coordination, exhibiting "high-high" and "low-high" spatial clustering, and demonstrating a pronounced positive spatial autocorrelation.(2) The integrated advancement of fintech and green finance substantially enhanced urban decarbonization.This effect exhibited regional heterogeneity, which showed the most pronounced in the lower reaches, followed by the middle reaches, and least evident in the upper reaches.(3) Urban industrialization and green technological innovation exhibited both first-order and second-order threshold effects on the synergistic promotion of urban decarbonization, indicating an increasing marginal effect.Drawing on the aforementioned conclusions, we propose certain policy recommendations aiming at establishing a novel green financial system, creating a synergistic framework for urban decarbonization, fostering the advancement of new industrialization, and bolstering green technological innovation.