Abstract: Based on the panel data of Beijing, Tianjin and 11 cities in Hebei from 2005 to 2019, this paper measures the per capita carbon dioxide emissions of each city and establishes an extended STIRPAT model including financial scale and financial efficiency. On this basis, the paper establishes mediation effect model and spatial Durbin model to explore the mechanism and spatial effect of financial development on per capita carbon dioxide emissions. The results show as follows: ① The expansion of financial scale increases the housing prices, pushes up the production cost of enterprises, affects the layout migration of traditional manufacturing, and thus curbs carbon emissions. ② The improvement of financial efficiency provides financing convenience for the expansion of industrial enterprises, and the resulting scale effect promotes carbon emissions. ③ The role of financial development in supporting technological innovation is not significant. ④ There exists negative feedback effect between the carbon emissions of the Beijing-Tianjin-Hebei cities, which is not conducive to the coordinated development of urban agglomeration's environmental governance. ⑤ Compared with the local effect, the influence of financial scale and financial efficiency on carbon emissions of neighboring cities is weaker. Based on the above findings, policy suggestions are proposed on speeding up the improvement of green finance system, promoting credit support for green innovation, and resolutely eliminating excess production capacity.