Objectives: The Longgang area, located in the coastal plain of southeastern Zhejiang, has a complex groundwater seepage field evolution due to historical seawater intrusion and anthropogenic impacts. This study examines its groundwater hydrochemical characteristics and evolution trends. Methods: The study collected a total of 43 water samples (surface water, phreatic water, confined aquifers Ⅰ and Ⅱ) in the study area. Combined with the data from four monitoring wells and historical water samples for comprehensive analysis. Multiple analytical methods were employed—including multivariate statistical analysis, hydrochemical diagrams, ionic ratios, saturation indices, and inverse hydrogeochemical modeling to investigate the spatiotemporal evolution characteristics of hydrochemistry in the region and elucidate the formation mechanisms of water quality. Results: ① Hydrochemical types of the study area: Phreatic water are dominated by Cl·HCO3—Na and HCO3·Cl—Ca·Na types; Confined groundwater(I) are Cl—Na type; Confined groundwater(II) are mainly HCO3·Cl—Na type. ② The aquatic environment of the study area is generally weakly to moderately alkaline, Cation abundance (avg.): Na+>Ca2+>Mg2+>K+, Anion abundance (avg.): Cl->HCO-3>SO2-4. ③ Surface water and phreatic water(domestic well) Primarily controlled by rock weathering and dissolution; Confined groundwater(II) and some phreatic water influenced by combined evaporative concentration and rock weathering; Confined groundwater(I) and most phreatic water significantly affected by evaporation. ④ Major groundwater components result from: dissolution of silicates and halite (rock salt), dissolution/precipitation of calcite and dolomite, formation via cation exchange adsorption. Conclusions: The findings provide significant guidance for the sustainable development and utilization of groundwater resources in the Longgang coastal area of southeastern Zhejiang.