Abstract: Chazi geothermal field is located in Southwestern Tibetan Plateau. The geothermal potential has been ascertained by field survey and geothermal drilling. The hydrogeochemical characteristics and isotopic composition of this geothermal field show that the underground water belongs to HCO₃-Na. The difference of ion concentration between hot water and cold water shows that they have different material sources and certain hydraulic relations. The isotope analysis of δD and δ¹⁸O determines that the major source of the geothermal water in this area is meteoric water and water melt from the mountains snow and ice with the height above 5 652 m. The geothermal water was the result of the mixture of deep infiltrated meteoric water and deep-source fluid when they move along the fracture zone. The fracture zone is the main channel of hot spring and the reservoir of geothermal fluid. The migration retention time of the geothermal water in this geothermal field was at least 41 years. According to the calculated temperature of SiO₂ geothermometer, the geothermal temperature of the underground heat reservoir is about 148.18~153.49 ℃, and natural heat discharge is 2 264.33×10¹² J/a.