Jiangxi has abundant hydrothermal geothermal resources, and the highest water temperatures are found in the geothermal waters of Lantian, Ningdu and Tanghu, Suichuan, with surface water temperatures of 79~86 ℃, which have good potential and perspectives for development and utilization. In this paper, based on summarising the research results of the previous researchers and field hydrogeochemical investigations, analyzing the geological and hydrogeological conditions of the geothermal areas, and carrying out systematic geothermal hydrogeochemistry and isotope geochemistry studies, we have made a more in- depth discussion on the characteristics of the medium- temperature geothermal waters of Lantian and Tanghu, and the causes of the geothermal water in these areas. The study shows that the chemical types of geothermal water in Lantian and Tanghu are SO2-4—HCO-3—Na+ type and HCO-3—Na+ type respectively, and their recharge sources are atmospheric precipitation, with the recharge elevations of 890~1100 m and 1040~1220 m respectively; the 14C ages of the geothermal water are 16.17±0.14 ka and 14.62±0.11 ka. The SiO2 geothermal temperature scale and geothermal gradient calculations show that the thermal storage temperature of geothermal water is 146.32℃ and 133.79℃ respectively, and the circulation depth is 3258 m and 2760 m. The geothermal water belongs to the atmospheric precipitation infiltration, the groundwater temperature increases with the geothermal temperature gradient to form underground hot water, and then hot water rises through the fracture to form the geothermal water on the surface of the atmospheric precipitation deep cycle genesis mechanism. The research results are of great theoretical significance and high academic value for revealing the genesis mechanism of mesothermal geothermal water in Jiangxi and its neighboring provinces.