Abstract: In the context of the “innovation-driven development” strategy, supply-side structural reforms and tax and fee reduction policies. Research on the economic effects of R&D expenses plus deduction policy has important theoretical and practical significance. This paper treats the promulgation of Cai Shui〔2015〕No.119 as a quasi-experiment, uses the listed companies in Shanghai Stock Exchange and Shenzhen Stock Exchange from 2008 to 2017 as research samples, applies the method of Difference-in-Difference (DID) to study, investigates the impact of R&D expenses plus deduction policy on total factor productivity of enterprises. This paper obtains the following conclusions: (1) The implementation of R&D expenses plus deduction policy can significantly increase the total factor productivity of enterprises. (2) The significantly positive impact of R&D expenses plus deduction policy on total factor productivity of enterprises is achieved by increasing the R&D investment of enterprises. (3) The effect of this policy varies significantly among enterprises in different regions, different scales, different levels of competition in different industries and different life cycles. Based on the above conclusions, this paper puts forward some suggestions to improve the policy of additional deduction of r&d expenses in China.