Abstract: Fujian Province is one of the most important geothermal anomaly areas in China. It is of great significance for the scientific utilization of geothermal resources to reveal the formation mechanisms of geothermal system in the region. The changes in hydrochemical formation and water-rock interaction mechanism of geothermal fluids in each hydrogeochemical zone was clarified based on the implication of hydrochemical characteristics of 208 geothermal water samples and the machine learning methods of self-organizing map-K-means (SOM-KM) clustering. The results show that the water types of geothermal fluids from the uplifted mountainous recharge areas to the low-lying valleys and deep basin axis evolved from HCO₃-Ca and HCO₃-Na·Ca to HCO₃·SO₄-Na and HCO₃-Na in each intact groundwater system in inland areas. While from the central mountainous areas to the eastern volcano-graben basin and coastal plain, the water types of geothermal fluids evolved from HCO₃-Ca, HCO₃-Na·Ca to HCO₃·SO₄-Na and HCO₃-Na, and then Cl-Na·Ca, Cl-Na type. The SOM-KM analysis identified the spatial distribution of low-enthalpy and low-salinity shallow circulating geothermal water, high-enthalpy and P-F-SiO₂ enriched deep circulating geothermal water, and deep circulation geothermal water with seawater mixing at the provincial scale effectively. Among them, the low-enthalpy shallow circulating geothermal water was significantly affected by the mixing of surface water and shallow groundwater, and mainly distributed along the steam systems of northwestern uplifted mountain region and the carbonate-clastic sedimentary basins of southeastern region. The hydrochemistry formation of high-enthalpy deep circulating geothermal water was significantly influenced by the upwelling mixing of endogenous water in igneous rocks, deep-seated faults, and ancient sealed fluids in volcanic edifice, and mainly distributed at the intersection of regional northwestern water-conducting faults with the northeastern thermal-conducting faults and the radioactive faults of the circular volcanic apparatus in eastern volcanic depression zone. The deep circulation geothermal fluid affected by seawater recharge undergone the first mixing process with the deep high-salinity seawater and the second mixing process with shallow cold water during the upwelling stage. The long-term supply endmember of hydrochemistry in regional intrusive-volcanic geothermal reservoir is plagioclase, and the reservoir temperature indicated by mineral hydrothermal alteration is concentrated in the range of 100-150℃. The geothermal fluid tended to evolve towards HCO₃-Nawater with high pH, low-Na concentration and high-Ca concentration under the constraints of supersaturation precipitation of calcite - carbonate buffer equilibrium system due to the preferential dissolution of olivine, pyroxene, and anorthite in the plagioclase. The geothermal system in the bulk horizons is turned out to be deep-circulation hydrothermal systems without magmatic heat source from the hydrogeochemical evidence.