Abstract: Groundwater inorganic nitrogen contamination is one of the most widespread water environmental issues in the Jianghan Plain. Agricultural activities constitute an important source of inorganic nitrogen in groundwater. However, in agricultural regions characterized by dense river networks, the sources, migration pathways, and transformation mechanisms of inorganic nitrogen in shallow groundwater recharged by precipitation and surface water remain insufficiently understood. Taking the agricultural area of the eastern Jianghan Plain as a case study, the chemical characteristics, the source of inorganic nitrogen, and its migration and transformation mechanism of surface water and groundwater were analyzed by hydrochemistry combined with hydrogen-oxygen and strontium isotopes. The results show that the cations of surface water and groundwater samples in the study area were dominated by Ca²⁺ and Na⁺, and the anions were dominated by \mathrmHCO_3^- .The water chemical type was dominated by HCO₃–Ca•Na and HCO₃–Ca. The inorganic nitrogen in surface water and groundwater was mainly nitrate, and the concentration of inorganic nitrogen in groundwater was significantly higher than that in surface water. The groundwater with high nitrate concentration was mainly distributed around the northern and southern towns, and the distribution of ammonia nitrogen with high concentration was scattered. Precipitation was the primary source of surface water and groundwater recharge in the region. The chemical characteristics of surface water and groundwater were mainly controlled by silicate and evaporite weathering, and were obviously affected by human activities. The surface water with extreme low concentration of inorganic nitrogen was mainly from atmospheric precipitation, while the groundwater with relatively high concentration of inorganic nitrogen was mainly from domestic sewage and feces in agricultural areas. The mutual transformation of inorganic nitrogen components was affected by the redox conditions. The inorganic nitrogen of the pollution source in the surface layer was mainly ammonia nitrogen, and the concentration of ammonia nitrogen in groundwater is high. Nitrate was gradually enriched by nitrification, accompanied by the downward migration of atmospheric precipitation. This study is of great significance for understanding the causes and migration and transformation mechanism of inorganic nitrogen enrichment in groundwater in agricultural areas with dense water networks, and for the prevention and control of groundwater pollution in Jianghan Plain.