Abstract: To improve the uniformity of underground temperature after using ground source heat pump system, three optimal layouts of 36-borehole heat exchangers (BHE) were proposed for area with an unbalanced cooling/heating load ratio of 2.5:1.0 and an operation duration of 20 years. Results show that the less the BHEs are located in the center of drilling area, the more uniform the temperature field with the less temperature gradient will be. The surrounding underground excess temperatures of the optimal layouts are slightly higher than that of the traditional layout and the peak values of the temperature field can be reduced. Additionally, the effect is more significant when applied to the area with small thermal diffusivity. The feasibility of the proposed optimal BHE layout are verified.