China's unprecedented urbanization is inextricably entwined with the story of the domestic “migrant flood.” The extent to which China's internal migrants are socially integrated into the host cities is often explained in reference to individual factors and the “context of reception” with the role of the migrants' origins generally overlooked. Drawing on the 2017 China Migrants Dynamic Survey, this paper describes how situational differences in economic development, cultural characteristics and population size between hometowns and receiving cities interact with individual-level variables to determine integration outcomes. We found that all three dimensions are negatively correlated with social integration and that the impacts of cultural characteristics and population size are conditioned on the migrants' hukou (household registration system) status. In addition, we supplement Gordon's classic assimilation theory by showing that whereas staying longer does facilitate cultural integration it fails to neutralize the negative impact of the economic gap and the population size. Our mixed results highlight that spatial inequalities generate formidable obstacles to social integration and may even be more challenging to overcome than the institutional constraint. It therefore underscores the importance of narrowing spatial inequalities and establishing favorable policies to improve the lived experiences of internal migrants in China.