Abstract: The Linyi segment of the Yishu fault zone is rich in geothermal resources with superior structural and geothermal geological conditions, showing great development and utilization potential. To reveal the genetic mechanism and evolution law of the geothermal system in this area, this paper takes the Tangtou and Yinan geothermal fields as research objects, and systematically analyzes the water-rock interaction, recharge source, reservoir temperature and heat supply mechanism of geothermal fluids by using hydrogeochemical analysis, geothermometer calculation and isotope analysis. The results show that the geothermal water in Tangtou is of Na-Ca-Cl type with TDS of 1 960~2 664 mg/L, while that in Yinan is of Na-Cl-SO₄ type with TDS of 1 583~2 900 mg/L. The hydrochemical components of geothermal water in both areas are controlled by rock weathering, cation exchange and dissolution-precipitation of halite. According to geothermometer calculations, the reservoir temperature in Tangtou is 87.88~101.69 °C with a corresponding circulation depth of 2 107~2 507 m, and the reservoir temperature in Yinan is 116.35~121.05 °C with a corresponding circulation depth of 2 930~3 066 m. Geothermal waters in both areas are originated from atmospheric precipitation. The recharge elevation of Tangtou is 315~900 m, which is inferred to be the middle-low mountains in the west/northwest (such as around Caimengding and Shichonggu). The recharge elevation for Yinan reaches 1 065~1 422 m, with Guimeng Peak - the highest summit of Mengshan Mountain - as the primary recharge source. Both areas belong to deep-circulation low-medium geothermal systems recharged by atmospheric precipitation. The differences are mainly caused by the terrain of recharge areas, the length of circulation paths, and the control of fault structures on the migration and evolution of geothermal fluids. The Yinan geothermal system has a relatively higher recharge elevation, deeper circulation depth, and stronger water-rock interaction and hydrochemical evolution. This study can provide a theoretical basis for the evaluation, exploration and sustainable development of geothermal resources in the Linyi segment of the Yishu Fault Zone.