Abstract: This paper established a 3D heat transfer model to simulate the running state of the vertical U-tube ground heat exchanger(GHE), which introduced the heat exchange function as the boundary condition for the inlet of the U-tube. The author proposed a new method to calculate the distance between individual line heat source and the district center, and derived the solution by finite volume method. The model can meet the requirement for the engineering precision by comparison between numerical and experimental results. Furthermore it presented the temperature distribution of the fluid inside the U-tube, and also analyzed the effects of the depth of borehole on thermal interference between the U-tube two legs.