Based on the law of mass and energy conservation and the one-dimensional model of heat transfer, a heat and moisture transfer line source model for the ground-source heat pump system has been developed. Numerical simulation results in summer working conditioning indicate that the affect of moisture transfer in soil was mainly around the U-type tube. When the soil moisture content is high, the capacity of heat transfer in soil is good. The heat transfer capacity of the ground heat exchanger calculated by the model in this work is lower than those which are calculated by the common heat transfer model. When the initial soil moisture content is about 0.1, the difference calculated by the two model is about 18%.