With the launch of the national carbon trading market, clarifying the relationship between carbon trading policy and enterprises' green technological innovation has profound policy implications for promoting enterprises' green transformation and sustainable development. This paper took the carbon trading policy as a quasi-natural experiment, selected the data of A-share listed enterprises in China's Shanghai and Shenzhen markets from 2010 to 2021, and used the multi-temporal double-difference model, the multiple intermediary effect model and the threshold effect model to explore the impact of the policy on enterprises' green technological innovations, to validate whether the carbon trading policy could produce innovation incentive effects and to explore its transmission mechanism. The results reveal that the carbon trading policy promotes firms to upgrade to green technologies, but this incentive impact has a time lag and a time restriction. The heterogeneity analysis shows that the promotion effect of carbon trading policy is more prominent in large enterprises and state-owned enterprises; the quantile regression results show that carbon trading policy can only be effective when enterprises' levels of green technological innovation reach a certain threshold. The mechanism analysis finds that the mediating variables financing constraints and R&D inputs have chain mediating effects and non-linear characteristics, and the green innovation effect of carbon trading policy is significantly enhanced after the enterprise financing constraints and R&D inputs pass the threshold. Carbon trading regimes have not been effectively promoting the degree of green technology innovation in small and non-state firms because of the finance restrictions' threshold impact.