The hydrogeochemical characteristics and evolution of geothermal fluids can reveal the deep circulation mechanism of geothermal water, which is of great significance for the development and utilization of geothermal resources. Based on the geothermal geological conditions of the Rongcheng geothermal field, this paper selects 16 deep geothermal well waters and 2 cold waters in the Baoding mountain area to analyze their hydrochemical characteristics and isotopes, calculate the temperature of thermal reservoir and depth of the thermal cycle. Finally, we undertake reverse hydrogeochemical path simulation to analyze the water rock reaction and migration process of geothermal fluid in the deep. The results show that the hydrochemical type of deep geothermal wells in the study area is of the HCO3·Cl- Na type, and that of Baoding mountain area is of the HCO3-Ca·Mg type. There is no significant positive correlation between Cl and almost all ions in the Rongcheng geothermal field, indicating that trace elements mainly come from the dissolution of related minerals. The high concentration of Na+ in the Rongcheng geothermal field indicates that the groundwater runoff is long and the depth of thermal cycle is large. The content of HBO2 is higher, which means that the runoff of geothermal water is smaller and the velocity is weaker. D and 18O isotopes are basically near the atmospheric precipitation line, and the calculated recharge elevation of geothermal wells is 665. 17~1165. 17 m, which is close to the altitude of the Baoding mountain area, indicating that the geothermal water sources in the study area are mountain front recharge and atmospheric precipitation. The deep thermal storage temperature is 57~98 ℃, and the depth of thermal cycle is 1331~2483 m. During the progress of the groundwater from the Baoding mountain area to a plain geothermal well, in addition to water rock action, a series of processes such as boiling, evaporation, mixing of cold water and precipitation supplementation have taken place, which makes the ion content of groundwater change greatly.