Understanding intercity population movement is vital for the socioeconomic development of urban areas. Based on Amap big data spanning 2019 to 2023, this study utilizes a combination of social network analysis and explainable machine learning techniques to explore the spatiotemporal patterns and determinants of intercity population movement across 368 cities in China. The findings highlight significant heterogeneity in the spatial distribution of population flow, characterized by a “southeast dense, northwest sparse” pattern, though spatial disparities have narrowed over the past five years. Population flow varied significantly across cities, with high-tier cities exhibiting contrasting net population inflow compared to low-tier cities. Hierarchical clustering patterns were evident, with the Beijing-Tianjin-Hebei region, Yangtze River Delta, and the Pearl River Delta emerging as primary hubs of population distribution. The population flow network demonstrated distinct community characteristics, with divisions closely aligned with geographical proximity and provincial-level administrative divisions. Basic regression analysis identified city population size, economic development, public service quality, and air quality as significant factors in population mobility. Further analysis using explainable machine learning techniques revealed that distance, high-speed rail connectivity, and population size were the most impactful determinants, displaying complex nonlinear relationships. Additionally, this study identified the evolution of nonlinear effects associated with key determinants over time. These findings advance the theoretical understanding of mobility mechanisms beyond linear assumptions and offer valuable insights for optimizing urban agglomeration structures and guiding mobility management policies.