Abstract: Abstract: As an important component of the underground heat exchange system, the performance of the coaxial heat exchanger in medium-deep geothermal wells directly determines the efficiency of geothermal energy development and heat extraction effect. In this paper, the relationship between the heat-insulating inner tube and the heat transfer performance of coaxial heat exchanger in medium-deep geothermal wells is investigated through field tests and numerical simulations, and the effects of the length of the inner tube insulation and the insulation scheme on the water temperature and heat extraction power of the coaxial heat exchanger are analyzed. The results show that the short-term heat extraction power of the coaxial heat exchanger is 1506.83 kW when a real aerogel insulated tube with a thermal conductivity of 0.06 W/(m·K) is used as the inner tube, and for a geothermal well of 3500 m depth, the thermal insulation performance of the inner tube decreases with increasing depth, and the thermal insulation performance of the 0～1400 m section has a greater influence on the overall heat transfer effect. Increasing the flow rate in the tube can reduce the effective insulation length of the inner tube. The results of the study can be used as a reference for the efficient development and utilization of medium and deep geothermal energy and the optimal design of coaxial heat exchangers.