As the problem of global climate change becomes more severe, countries have proposed the goals of carbon capping and carbon neutrality. Green finance is an essential capacity support for achieving carbon peaking and carbon neutrality, and it can guide and stimulate social capital to invest in low-carbon industries and initiatives via marketbased mechanisms. Based on the panel data of Chinese prefecture-level cities from 2006 to 2020, this paper empirically examines the impact of green finance on carbon emission efficiency using a two-way fixed-effects model, conducts a regional heterogeneity analysis, and examines the threshold effect of economic development level and the mediating role of regional innovation. The results indicate that, first, green finance contributes significantly to the improvement of carbon emission efficiency, and second, the level of regional economic development has a double threshold effect on the contribution of green finance to the improvement of carbon emission efficiency. Third, regional innovation is an important green finance channel for influencing carbon emission efficacy. The sensitivity of carbon emission efficiency to the green finance index demonstrates an inverted U-shaped trend. Fifth, the importance of green finance sub-dimensions in relation to carbon emission efficacy is as follows: green support, green credit, green insurance, green investment, green equity, green bond, and green fund. These findings provide theoretical support for green finance's role in promoting co-carbon efficiency and are valuable for policy formulation.