Abstract: The Guanshan River, an important incoming tributary of the Danjiangkou Reservoir, serves as the crucial water source for the Middle Line of the South-to-North Water Diversion Project. Mathematical statistics, Piper trilinear plots, Gibbs models, principal component analysis (PCA), and the stable isotopes of hydrogen (δD) and oxygen (δ18O) were used to explore the hydrochemical types, the spatial distribution characteristics and influencing factors of ions. The results indicated that the pH value of Guanshan River was between 7.38 and 8.91, which was moderately alkalescent. The TDS ranged from 122 to 265 mg/L and the physical and chemical properties of the main stream were affected by the influx of tributaries. The chemical characteristic was the "Ca-HCO3" type, with Ca2+ being the primary cation, accounting for 51% to 70% of the total, and HCO3- being the primary anion, accounting for 49% to 83%. The characteristics of hydrogen and oxygen isotopes, deuterium excess value and ion concentrations revealed that atmospheric precipitation was the main recharge source of surface water, and evaporation was also an important factor controlling hydrochemical characteristics of Guanshan River. The hydration characteristics of rivers were predominated by the weathering of carbonate and silicate rocks. Carbonic and sulfuric acid were the primary acidic media contributing to the weathering of rocks in the basin. Ion exchange was an important reason for the high Na+/Cl- ratio in river. Nitrate was to some extent affected by human activities such as domestic sewage discharge. Generally, anthropogenic activities had a little impact on the Guanshan River, due to the aquatic environment protection measures taken in the water source area of the South-to-North Water Diversion project.