Abstract: The emergence of new trends and policy propositions such as ’in-situ urbanization’ and ’countylevel urbanization’ has endowed systematic comparative research on China’s urban-rural population mobility between 2000 and 2020 with significant theoretical value and practical relevance. Based on the national population censuses of 2000, 2010, and 2020, this study reveals the evolutionary trajectory of urban-rural spatial patterns in population mobility over this two-decade period. Preliminary findings indicate three national-level phenomena: intensified ’polarization at the apex’ and ’ossification in the mid-tier’ of China’s urban hierarchy; accelerated ascendance of medium-sized county seats as core platforms for county-level urbanization; and increased demographic contributions from migrant populations to both apex cities and county towns, contrasted with diminished contributions to mid-sized cities. At the regional scale, the analysis concentrates on primary population inflow and outflow areas, investigating four dimensions: spatiotemporal evolution of urban-rural population distribution, spatial characteristics of migrant populations, disparities in urban system structures, and differentiated migration patterns across cities and towns. The study further explores causal mechanisms through three analytical frameworks-economic dynamics, institutional evolution, and socio-cultural drivers-while proposing future research directions informed by these findings.