Low-carbon policy tools are an important part of the "two-carbon" strategy. How to use low-carbon policy tools to promote win-win economic and environmental protection? In this paper, the panel data of 30 provinces (municipalities and autonomous regions) in mainland China from 2010 to 2021 are used to systematically investigate the impact and mechanism of low-carbon policy tool synergy on green technology innovation. It is found that low-carbon policy tool synergy significantly stimulates green technology innovation. Robustness test is conducted by alternative variable test, propensity score matching and instrumental variable method. This conclusion is still valid. Meanwhile, the impact of low-carbon policy tool synergy on green technology innovation is heterogeneous due to differences in geographical distribution, environmental regulation and environmental pollution degree. The spatial spillover effect analysis shows that low-carbon policy tool synergy has positive spatial spillover effect on green technology innovation. The regulatory effect analysis shows that the GDP-led local government competition has a negative regulatory effect on the relationship between low-carbon policy tool synergy and green technology innovation.