Based on the background of science and technology investment system under Chinese fiscal decentralization，this paper selects panel data of 30 provinces and municipalities in China from 2008 to 2016 to construct a spatial Tobit model to empirically test the impact of local government competition on the efficiency of fiscal investment in science and technology and the moderating effect of legal environment. The study finds that the efficiency of fiscal investment in science and technology has spatial agglomeration and spatial spillover effect. Government competition has a promoting effect on efficiency and efficiency spillover，and this promoting effect has spatial heterogeneity. Specifically， for the provinces，regions and cities in the eastern and central regions， intergovernmental competition not only brings about the improvement of efficiency within their jurisdiction，but also contributes to the spillover of efficiency， while the intergovernmental competition in the western provinces not only inhibits the improvement of efficiency within their jurisdiction，but also has a negative impact on the efficiency of fiscal investment in science and technology in the surrounding areas.Further research finds that the efficiency improvement in investment in science and technology brought by competition among local governments has a strong environmental dependence. The better the legal environment is，the more prominent the role of competition among local governments in promoting the efficiency and efficiency spillover of financial investment in science and technology is.