Public service is not only an important indicator to improve people''s living standards, but also reflects the development level of a city. In this paper, the county economic development as the research object, the county public service scientific analysis, from the two perspectives of trade facilitation and government development, in-depth study and analysis of the impact mechanism of public service supply on the county economic transformation through foreign investment. At the same time, the economic data of 1126 counties in 17 provinces along the “Belt and Road” were selected for data analysis and measurement inspection. The results showed that: in the transformation of county economy, the promotion of direct public service is not obvious, but it can indirectly play a more significant role through the introduction of foreign investment. In addition, one belt, one road strategy, has promoted the direct effect of direct public services on the transformation of county economy. Social and business public services have generated positive spillovers in the transformation of county economy through foreign investment, resulting in excessive siphon effect on local resources and thus affecting the economic development of neighboring counties.