In 2015, China started the process of the merger of national and local tax authorities. This paper uses private listed companies from 2002 to 2019 as the research sample, and uses the fuzzy regression discontinuity to study the effect and mechanism of tax competition on the investment efficiency of Chinese private enterprises after the merger of national and local tax authorities. The study shows that the merger of national and local tax authorities has improved the level of tax collection and management, thereby inhibiting malicious tax competition among local governments, optimizing the business environment, and improving the investment efficiency of private enterprises. In the future, the Central Government of China should pay more attention to the realization of social public interests when making rules, and the tax competition among local governments should also properly manage the issue of "degree". In addition, it is necessary to comprehensively assess the international situation and impact, examine the economic effects of tax competition from the perspective of international economic relations and economic globalization, and rationally choose tax tools according to the goals of equalization of public services and coordinated regional development.