Based on the two-dimensional heat transfer model for single U pipe in GSHP (Ground Source Heat Pump) system, this paper analyzed the influences of main different multi-variables on the heat resistance, including the heat conductivity coefficient of backfill materials, the buried pipe spacing in the borehole and the water velocity in the pipes.Improved Genetic Algorithm (IGA), in which elitism selection and migration were combined, was used to optimize the heat resistance in the borehole based on foregoing multi-variables.According to the optimized result, the minimum heat resistance was obtained when the heat conductivity coefficients of backfill materials, the buried pipe spacing and the water velocity in the pipes reached their maximal designed values.The results are useful for the optimization of the heat exchanger design of GSHP.