In order to systematically analyze the phenomenon of internal migration from a demographic perspective and identify its trends, this study constructs a comprehensive understanding of internal migration through the respective approaches of migration flows, migrants, and regions (origin & destination). The overall characteristics of internal migration are analyzed under seven themes. The main findings include the decline in total migration, the actual extent of population change in regions, the characteristics of migration in population crisis regions, confirmation of the cascading migration hypothesis, the gender dimension of rural youth outflows, the evolution of migration in population crisis regions, analysis of the characteristics of migrants moving in and out of population crisis regions, and the aggregate socio-economic impacts of migration on population crisis regions. These findings emphasize that responses to regional population crises have to be based on a comprehensive understanding of population movements and the structure of inter-regional relations.