Midu County, Dali Prefecture is rich in geothermal resources, where hot springs are developed, but the degree of development and utilization is low.【Objective】To reveal the genetic mechanism of geothermal water in the county and provide a basis for the development and utilization of hot spring resources.【Methods】This study selected five hot springs, two cold springs, two surface water samples, and one well water sample as research objects. Hydrogeochemical methods, isotope characteristic analysis and geothermal reservoir characteristic analysis were adopted to infer the genesis of hot springs, and use COMSOL Multiphysics software to perform numerical simulation of typical profile hot spring water thermal coupling.【Conclusion】The results show that: The hydrochemical type of geothermal water in the study area is mainly HCO3-Na type water, supplied by atmospheric precipitation, with an average supply elevation of 2827 m. The supply area is located near Shuimu Mountain in the eastern part of the county and Bijia Mountain in the northwest. There is a significant "18O drift" phenomenon in the water samples, indicating that geothermal water has undergone a certain degree of oxygen isotope exchange. The groundwater age in the study area is between 1067a-28313 a, there are significant differences in the retention time of different hot spring cycles.The temperature of geothermal reservoir is between 81-114℃, and the depth of geothermal water circulation is between 2387-3487 m. The two-dimensional simulation results of hydrothermal coupling in typical sections show that the seepage field presents obvious hierarchical pattern. The temperature field shows that the heat exchange occurs with the rock mass after rainfall infiltration into the formation, and the heat in the bottom high-temperature stratum is carried to the shallow part and the spring is exposed at the fault. The cause of thermal water can be summarized as follows: atmospheric precipitation seeped down the outcrop of aquifer, gradually heated by heat exchange with surrounding rock in the process of infiltration and migration from shallow part to deep part. When it reached a certain depth, it encountered faults and migrated upward along the fault zone. In the upward migration, due to the dilution effect of surface cold water, the water temperature dropped, and finally rose to the surface along the tensile fault zone or fracture fracture zone, and emerged into springs. The study reveals the formation reasons of geothermal water in Midu County, which can provide important basis for the development and utilization of hot springs and the protection of geothermal water resources in the study area.
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