Abstract: As a product of the deep integration of science and technology and finance, Sci-Tech Finance, with its innovative capabilities and resource integration strengths, offers innovative ideas for facilitating the green transformation of the economy and society and enhancing environmental governance efficiency. Using the "Promoting the Integration of Science and Technology with Finance" pilot policy as a quasi-natural experiment, this paper leverages panel data collected from 282 prefecture-level cities across China over the 2006−2022 period and utilizes the staggered difference-in-differences (DID) model to examine the impact of Sci-Tech Finance policies (STFP) on the synergy between pollution reduction and carbon mitigation (SPRCM), as well as the underlying mechanisms. The results indicate that: STFP significantly promotes urban SPRCM. Green technological innovation, industrial structure optimization, and financial resource allocation efficiency constitute key mechanisms through which STFP facilitates SPRCM. Heterogeneity analysis reveals that STFP exerts a more pronounced promoting effect on SPRCM in non-resource-based cities, key environmental protection cities, and cities with high-level digital transformation. The findings provide policy insights for fully the effectiveness of STFP and achieving synergistic urban governance in pollution reduction and carbon mitigation.