Situated in the unique Chinese context of rapid urbanization and mass migration, this study draws on 4 waves of data from the China Family Panel Studies (CFPS) spanning from 2012 to 2018, employing propensity score matching and weighted least squares regression to identify the causal relationship between rural-to-urban migration and subjective well-being, along with its intermediate pathways. The results show that rural-to-urban migration follows a positive selection process, with migrants exhibiting more advantageous socioeconomic characteristics before migrating; furthermore, such migration has a significantly negative impact on life satisfaction; social psychology, family relations, and working environment mechanisms partially account for the well-being deterioration caused by rural-to-urban migration; short-term and intra-provincial migration have more pronounced negative impacts compared to long-term and inter-provincial migration. Taken together, our findings inform effective policies designed to promote urban-rural integration and realize common prosperity, such as establishing a comprehensive well-being assessment system, improving social integration and solidarity within urban communities, developing family support and educational services, and regulating corporate employment practices.