Abstract. The transforming relationship between surface water and groundwater as well as their origins are the basis for studying the transport of pollutants in river-groundwater systems. A typical section of the river was chosen to sample the surface water and shallow groundwater. Then, a Piper trilinear diagram, Gibbs diagram, ratios of major ions, factor analysis, cluster analysis and other methods were used to investigate the hydrogeochemical evolution of surface water and groundwater and determine the formation of hydrogeochemical components in different water bodies. Based on the distribution characteristics of hydrogen and oxygen stable isotopes δD and δ₁₈O and discharge hydrograph separation methods, the relationship between surface water and groundwater in the Weihe River was analyzed. The results indicated that the river water is a SO₄·Cl—Na type and that the groundwater hydrogeochemical types are not the same. The dominant anions are HCO₃⁻ in the upstream reaches and are SO₄²⁻ and Cl⁻ in downstream reaches. Hydrogeochemical processes include evaporation and concentration, weathering of rocks, ion exchange, and dissolution infiltration reactions. The δD and δ¹⁸O of surface water change little along the river and are more enriched than are those of the groundwater. With the influences of precipitation, irrigation, river recharge and evaporation, the δD and δ¹⁸O of shallow groundwater at different sections are not the same. There is a close relationship between the surface water and groundwater. Surface water supplies the groundwater, which provides the hydrodynamic conditions for the entry of pollutants into the aquifer.