Accurately identifying the impact of population inflow on the level of basic public services is an important prerequisite for the rational allocation of public service resources, the orderly guidance of the spatial transfer of labor, and the promotion of high-quality and coordinated development of new urbanization. It is necessary to combine the 2005-2018 data of the main population inflow areas-70 large and medium cities across the country- and the urban settlement threshold index to measure the basic public service levels of each city and conduct regional differences analysis. Based on the spatial panel model and instrumental variables Law, this paper empirically examines the impact of population inflow on the level of basic public services, and analyzes the heterogeneity of cities of different scales. The results show that the overall level of basic public services in Chinese cities has been facilitated, the differences between cities have been improved, and regional imbalances have been significantly reduced; the impact of population inflow on the level of basic public services in the inflow areas has a certain lag, but in the long run, the “scale effect” of population inflows in China will eventually exceed the “crowding effect”, thereby significantly improving the level of local basic public services. Further research also finds out that the impact of population inflow on the basic public service levels of cities of different scales is different. It mainly shows the “crowding effect” for super large cities, while it is more prominently shown as the “scale effect” for other cities. Population inflow will have a negative spillover effect on the level of basic public services in neighboring cities. Regional GDP per capita, urbanization rate of the permanent population, and local government financial autonomy can all significantly improve the level of basic public services in the inflow areas. The above conclusions not only enrich the research of basic public services, but also provide a significant inspiration for ensuring and improving people’s livelihood and promoting regional coordinated and sustainable development.