This paper uses the endogenous growth theory and spatial durbin model to empirically study the dynamic factors, mechanism and spillover effect of the common prosperity by the digital economy, which constructs the index system to comprehensively evaluate the common prosperity from the dimensions of social security, welfare and development. According to the panel data of prefecture-level municipality in the Yangtze River Delta from 2011 to 2020, the research results show that: (1) The digital economy has the spatial spillover effect on the development of common prosperity by activated data element resources and enhanced the digital readiness through information infrastructure construction, which can achieve the inclusive development of “the Rich First Pushing Those Being Rich Later”. (2) The digital economy accelerates the nonlinear growth of common prosperity to obtain the achievement of “Enlarge and Divide the Cake” by the threshold effect of social welfare level and advanced industrial structure level. (3) The digital economy enhances the digital literacy and promotes “cultural common prosperity”, which the digital talent training policy consolidates the social cultural gene by the multi-period difference-in-difference model.