One of the main deployment forms of geothermal energy is the soil source heat pump system. In this paper, the variation of the heat transfer characteristics of the double U-tube heat exchanger underground are analysed based on the soil source heat pump system (SSHP) experimental system, which was installed with six temperature measuring cables with a total of 117 DS18B20 soil temperature measuring points. Based on the same working conditions (the initial soil temperature was 14.5°C, the initial inlet water temperature of the U-tube pipe was 3°C, the flow rate was 120L/h and the corresponding flow velocity was 1.7m/s), the thermal interference of the double U-tube pipes underground was studied during the operation of the soil source heat pump, the soil heat transfer characteristics between single and double U-tube pipes were compared. Furthermore, the effects under different seepage velocity on soil temperature field were studied, the heat transfer rate underground analysed and the variation regulation of heat interference explained. It can be concluded that the thermal radius of the single U-tube system was greater than that of the intersection area of the double U-tube pipes field of the system. The greater the seepage velocity, the greater the radius of action of the buried pipe on the soil along the direction of seepage. The thermal radius was smaller than normal at the direction of vertical to the seepage, and the greater the seepage velocity, the smaller the thermal radius applied by the buried pipe to the soil.