Abstract: The genetic mechanisms of medium-low temperature fault-controlled geothermal systems in the Western Jiangxi region of South China are complex, where deep circulation pathways and reservoir structures remain poorly constrained, hindering the precise exploration and sustainable development of geothermal resources. The Wentang geothermal field, located in the central section of the Wanlongshan fault zone in the northern part of the Luoxiao Mountain Range, represents a key site for elucidating the genesis of such geothermal systems. In this study, a total of 12 water samples were collected from the Wentang geothermal field. Through integrated application of geological structural analysis, hydrochemical diagrams, stable isotope (H-O-Sr) tracing, and geothermometers, the recharge sources, circulation evolution, and reservoir characteristics of the geothermal fluids were systematically investigated. The results indicate that: (1) Both the geothermal and cold waters in the study area are of meteoric origin. The geothermal water has undergone significant water-rock interactions during its flow path and has mixed with shallow cold water to varying degrees, with estimated mixing proportions ranging from 72% to 83%. (2) Quartz geothermometers estimate a deep reservoir temperature between 92.5℃ and 101.1℃. The hydrochemical characteristics classify it as a medium-low temperature, weakly alkaline, HCO₃-Na type water. (3) Comprehensive analysis reveals that the thermal reservoir structure is zonally distributed along the Wanlongshan fault zone, characterized as a fracture-pore composite reservoir with efficient heat conduction and accumulation capabilities. This study establishes a genetic model for the fault-controlled geothermal system described as “precipitation infiltration–fault-controlled deep circulation–heat conduction and accumulation–mixing of cold and hot waters”. It elucidates the synergistic heat-controlling mechanism involving structure, lithology, and fluid, thereby providing a theoretical foundation for the exploration and development of similar geothermal resources in South China.