Based on double U-tube heat exchangers of an actual construction in Changsha, a simulation model of ground heat exchangers was built up with the help of software TRNSYS. Combining the simulation model and orthogonal design, this paper studied the factors affecting soil average temperature around double U-tube heat exchangers, and analyzed effect degree of these factors. The results showed that borehole depth, borehole spacing, borehole amount and fill thermal conductivity had different influence on soil average temperature, and borehole spacing effect was particularly obvious. Finally, value range of borehole depth, borehole spacing and fill thermal conductivity were presented orderly as follows: 60~100 meters,4~5 meters,1.7~2.1 W/(m·K).