Yizhang, located in south of Hunan province of China is rich in geothermal resources. This paper aimed to study the concentrations
of cations, e.g., K+, Ca2+, Na+, Mg2+ and conducted the analysis of the environmental isotope characteristics of δD, δ18O and 13C.
Further there are explained the rules of the generation and evolution of geothermal groundwater in Yizhang. The temperature of
geothermal groundwater in Yizhang was between 34.2 and 45.4 °C, with a neutral pH and a high electrical conductivity. The
hydrogeochemical characteristics changed in the order HCO3-Ca, HCO3-Ca, HCO3-SO4-Ca, SO4-Ca-Mg corresponding to surface
water–underground cold water–Yongkou hot springs–Yiliu hot springs in Yizhang area. Compared with that in Yongkou area, the
water-rock interaction of groundwater lasted for a longer time in a more enclosed environment in Yiliu area. The δD-δ18O isotope
analysis showed that the geothermal groundwater was generated from atmospheric rainfall and the recharge height of geothermal
field was between 695~1040m. The 13C isotope analysis demonstrated that the CO2 generated during water-rock interactions was
induced by factors of biogenetic, atmosphere, mantle and carbonate rocks degeneration. The result of this study was that the
geothermal groundwater in Yongkou and Yiliu was formed from the same thermal resource in the same environment. Our research
contributed to the determination of the border of geothermal groundwater fields, the modelling of the geological thermal reservoir
structure, and the environmental evaluation of the groundwater in Yizhang, Hunan province, China.