The Ground Source Heat Pump system with pile heat exchangers has been used in engineering in recent years. In this paper, a three-dimensional numerical model of double-U pile heat exchangers is established which was verified through the comparison with ground thermal response test results. The influencing factors for the heat exchange performance of double-U pile heat exchangers are analyzed including pile depth, inlet temperature, initial ground temperature and ground thermal conductivity. An improved method is proposed on the basis of the cylindrical source model, combining with the numerical model. The improved method which is simpler than general analytical model can be used to obtain the ground thermal properties and thermal resistance of energy pile.