The utility model discloses a geothermal well water stop structure. Wherein the guide sealing assembly and the water stop ring assembly are sequentially arranged on an inner sleeve in a sleeving modefrom top to bottom. The lower end face of the guide sealing assembly is in sealing fit with the upper end face of the water stop ring assembly. A fixing flange is arranged at the upper end of the guide sealing assembly, the fixing flange is fixedly connected with the inner sleeve, and an elastic supporting assembly is arranged at the lower end of the water stop ring assembly and fixedly arranged on the inner sleeve to fixedly support the water stop ring assembly. By adopting the mode of combining the guide sealing assembly and the water stop ring assembly, it can be guaranteed that the water stop structure has a very good closed water stop effect, very good stability and reliability are achieved, and the use cost is low.