Abstract: With the intensification of global climate change and human activities, water quality pollution has become one of the important environmental problems facing the world. As one of the most economically developed and densely populated regions in China, the rapid urbanization and industrialization process in the Beijing-Tianjin-Hebei region has led to increasingly severe problems of water resource scarcity, deterioration of water quality, and degradation of water ecology. In this paper, total phosphorus output (TP) is used to measure the water quality purification function, and InVEST model, spatial autocorrelation analysis and spatio-temporal geographically weighted regression (GTWR) model are used to analyze the spatial and temporal evolution characteristics of the water purification function in Beijing-Tianjin-Hebei region and the spatio-temporal heterogeneity of the influencing factors. The results show that: 1. the phosphorus output in the northwestern mountainous areas is lower than that in the southeastern plains, and the high value areas are mainly distributed in the mountainous plains, and the temporal difference of phosphorus output from 1990 to 2020 is not significant, and the phosphorus output per unit area shows a decreasing tendency, which indicates that the water-quality purification capacity of Beijing-Tianjin-Hebei region has been strengthened; 2. the phosphorus output shows a significant “high - high” and “low-low” aggregation characteristics; 3. Spatio-temporal geographically weighted regression model (GTWR) analysis results show that, in general, the factors that have a large positive effect on phosphorus output are, in order, elevation (0.38), precipitation (0.29), IJI (0.10), and PD (0.09), and those that have a large negative effect are, in order, NP (-0.5), IJI (0.10), and PD (0.09). were NP (-0.50), population density (-0.42), PARA_MN (-0.31), and PRD (-0.25), in that order. Based on the spatial and temporal heterogeneity of the influencing factors, suggestions for the rational allocation of water resources and water environment management were made from three aspects, including natural environment management, industrial structure transformation and landscape pattern optimization, with a view to providing a reference for the high-quality development of Beijing-Tianjin-Hebei.