Abstract: The heat transfer of ground heat exchanger,comprising four vertically-buried U-tubes,of ground-source heat pump air-conditioning system,was empirically approximated,mathematically modeled,theoretically analyzed and numerically simulated with CFD software.The influence of the realistic situation,including,but not limited to the thermal properties of ground soil,cold and heat loads of building,and summer/winter seasons,on the heat exchange characteristics and temperature field distributions was investigated.The simulated results show that the seasonal thermal properties of ground-soil have a major impact.To be specific,in summer,the heat exchange per unit-length was 60.4 W/m,being 2.2% smaller than the theoretical prediction;and the radial/axial distributions of temperature field were calculated,respectively.Moreover,the ground temperature was found to decrease by 2.1℃ after shut-down of ground-source heat pump for 90 days.