The policy of adding deduction for R&D expenses has a broad impact on high-tech enterprises, especially on their innovation activities.High-tech enterprises from 2014 to 2023 was taken as the research object to examine the impact of the R&D expense plus deduction policy on enterprise innovation. The results of the study show that enhancing the intensity of the policy has a more significant incentive effect on both R&D investment and innovation ability of high-tech enterprises. These effects are heterogeneous in terms of enterprise size, that is the incentive effect on innovation is better for large-scale enterprises. Based on the conclusions of the study, it is recommended to further increase the proportion of R&D expenses plus deduction, optimize the design of tax incentives to take into account enterprises of different sizes, and establish a perfect policy evaluation and feedback mechanism to provide a good platform for enterprise innovation.