We analyse the causes of unbalanced development on both sides of the Hu Line and seek to narrow the gap in regional economic development levels. Achieving common prosperity is the fundamental principle, ultimate goal and basic requirement of socialism with Chinese characteristics. In this study, a total of 48 cities on both sides of the Hu Line are selected as samples, and an assessment system covering 18 indicators based on 8 aspects is constructed. A regression discontinuity method is adopted to test the differences in regional development on both sides of the Hu Line. The results show that the breakpoint effect on both sides of the Hu Huanyong Line is very obvious and that there is a significant imbalance in development, which is mainly reflected in eight aspects: population, economic output, finance, public finance, educational resources, employment, medical facilities, and urban development and construction. The results suggest that a large amount of work should be performed to increase fiscal support, strengthen public facility construction, improve medical and health levels, enhance investment in human capital and education, and accelerate the urbanization processes on the left side of the Hu Huanyong Line.