Abstract: Yuxian Basin has rich geothermal resources and complex geological structures. The study on the hydrochemistry, isotope and circulation characteristics of geothermal fluids controlled by geological structures can further promote the development and utilization of geothermal resources and geothermal hot spring health care industry around the capital city. By combining groundwater and atmospheric precipitation, and using multivariate statistics, correlation and characteristic coefficient analysis, the authors studied the geothermal fluid in Yuxian Basin using Piper triplex diagram and Na-K-Mg triangle diagram. The results are as follows. ① The cations in geothermal fluid are mainly Na⁺, Ca²⁺ and Mg²⁺, and the anions are mainly HCO₃^- and SO₄^2-. Ca²⁺, Mg²⁺ and HCO₃^- are mainly derived from the dissolution of carbonate minerals. ② A cation alternat adsorption occurred in geothermal fluid, with the action direction of K⁺, Na⁺ into the liquid phase, and Ca²⁺, Mg²⁺ into the solid phase. Na⁺ and Ca²⁺, Mg²⁺ are in a state of mutual inhibition. ③ The thermal reservoir formation is poorly sealed, the concentration degree and metamorphism degree of geothermal fluid are low, indicating a significant affection by infiltration water and shallow surface oxidation. The main source of geothermal fluid recharge is atmospheric precipitation, and the runoff path is short with fast water cycle. ④ The heat storage temperature was 37.32~57.36 ℃, the maximum circulating depth of heat storage in Wumishan Formation of Jixian System was 1 715~2 640 m, and the maximum circulating depth of the heat storage in Gaoyuzhuang Formation of Jixian System was 3 291~3 337 m, with the average value of 3 314 m. The interaction between groundwater and rock under geological structure was revealed, which could provide certain guidance in studying the hydrochemical evolution and dynamic characteristics of geothermal fluid in this area.