This study collected surface water samples from Chongqing in April， July， and December 2023 for physicochemical analysis. By integrating methods such as Piper trilinear diagrams， Gibbs semi-logarithmic plots， and ion ratio analysis，it aims to reveal the hydrogeochemical characteristics and spatiotemporal variation patterns of surface water in Chongqing， as well as the impacts of natural factors and human activities on its chemical composition. Results show that the pH of water samples across the three months is generally weakly alkaline. The dominant cation in Chongqing’s surface water is Ca 2+， while the primary anion is HCO - 3. The majority of regions exhibit a Ca-HCO 3 or Ca(Mg)-HCO 3 hydrochemical type. Overall， the hydrochemical characteristics of surface water in the study area are primarily influenced by evaporation-crystallization and rock weathering， and the ions are mainly derived from rock weathering. Seasonal variations reveal significant changes in the mass concentrations of cations and anions， total dissolved solids， and electrical conductivity， generally showing lower values during the rainy season compared to the dry season， mainly due to the increased rainfall during the rainy season. Spatially， higher NO - 3 concentrations are observed in southeastern and northeastern Chongqing， closely associated with agricultural activities; whereas elevated SO 2- 4 levels in western and central Chongqing are primarily linked to industrial activities. Overall， the concentrations of dominant ions Ca 2+ and HCO - 3 are mainly controlled by rock weathering， while SO 2- 4， NO - 3， and Cl - are significantly affected by various human activities， exhibiting distinct spatiotemporal patterns. These findings provide valuable insights for water resource protection and pollution control in Chongqing， contributing to improved water quality and sustainable urban development.