Under the background of double carbon, the medium-deep geothermal energy heating technology plays an increasingly important role in promoting energy conservation and carbon reduction in the construction field. As the core component of 'non-interference' geothermal energy exploitation, the structural parameters of the middle and deep coaxial casing heat exchanger have a profound impact on the heat extraction capacity of geothermal wells. Therefore, the numerical model of the coaxial tube heat exchanger with spiral fins on the inner wall of the outer tube was established by COMSOL numerical simulation software, and the correlation of Gnielinski and Konakov was used for verification and analysis. The effects of fin height, thickness, number, helix angle and their interaction on the heat transfer performance and flow resistance of the heat exchanger were discussed by using the response surface method. The parameter optimization of the structural parameters of the coaxial tube heat exchanger was carried out by using the satisfaction function method. The results show that when the fin height is 6 mm, the thickness is 2 mm, the number is 16, and the helix angle is 15°, the overall satisfaction is 0.75, the performance evaluation criterion(PEC) is 1.32, and the Nu under this structure is 39.00% higher than that of the ordinary mid-deep coaxial casing heat exchanger. In the analysis of the dynamic heat transfer performance of geothermal wells, the cumulative extracted heat of geothermal wells using the new coaxial casing heat exchanger is 12.87% higher than that of ordinary geothermal wells. The research results can provide new ideas and methods for enhancing the applicability of medium-deep coaxial casing heat exchangers, and can also provide reference for the design of the same type of medium-deep coaxial casing heat exchangers.