Abstract: Nanyi Gully is an important water source conservation area in Linzhi. The study of hydrochemistry and hydrogen and oxygen isotope characteristics of Nanyi Gully water body reveals the law of “three water transformation”, which is of great significance for improving the hydrochemistry research degree, supporting the research on the relationship between local forests and water, and serving the protection of water ecology in the plateau area. The characteristics of regional water chemistry, water-rock interaction and water cycle were analyzed by water chemistry and hydrogen and oxygen isotope analysis methods. The results show that water body of Nanyi Gully is very low salinity fresh water. The chemical types of surface water are HCO₃-Ca·Mg type and SO₄·HCO₃-Ca·Mg type, and the chemical types of the underground water are HCO₃-Ca·Na type. The hydrochemical characteristics of surface water and groundwater are mainly affected by the weathering of rocks, and the ions source is mainly affected by the carbonate dissolution and silicate rocks weathering. Na⁺, K⁺, Cl^- ions mainly come from the dissolution of evaporative salt rocks, which is also affected by the rainfall. The Ca²⁺ and Mg²⁺ mainly come from the dissolution of carbonate rock minerals. The water-rock interaction of the underground and surface water in the study area is weak, and most of the δ¹⁸O and δD values have obvious height effect and continental effect compared with the surface water in Yarlung Zangbo River and Lhasa River. The strong unbalanced evaporation during dry years is one of the main reasons for the small slope and intercept of the regional atmospheric rainfall line.