Abstract: From the perspective of common prosperity, this study re-examines the non-linear impact of social security expenditure on the urban-rural income gap based on the provincial panel data from 2001-2021. The results show that there is an inverted U-shaped relationship, first expanding then shrinking, between the social security expenditure and the urban-rural income gap, in which the degree of“sharing”of the social security benefits between urban and rural residents plays a mediating role. Further investigation in different regions reveals that this inverted U-shaped relationship also exists, that the inverted U-shaped curve of the central and western regions is wider, that the marginal impact effect of social security spending is greater, and that the social security expenditure at the inflection point of the curve is even more. Therefore, in order to effectively narrow the urban-rural income gap, it is necessary not only to reverse the urban bias existing in the social security expenditureand improve the degree of“sharing”of social security benefits between urban and rural residents, but also to continuously increase social security expenditure to improve the degree of“prosperity”of social security, as well as to pay attention to the adjustment of the regional bias of social security expenditure and increase the social security input in the central and western regions.

Key words: common prosperity, social security, income distribution, urban-rural income gap