The simulation results of a solar assisted ground coupled heat pump are presented in this paper to study the energy saving measures for space heating in northern China. Optimization on the solar collecting subsystem is implemented by investigating the influence of different parameters of the system. The optimization model of the system is developed under the TRNSYS environment, and the transient numerical simulation is carried out. The operating characteristic of the heating system is analyzed for a heating season in Beijing area. From the results of the simulation, the energy efficiency of the heating system and the operation stability of the system are improved with solar energy assistance due to recharging boreholes and direct space heating through the storage tank. Thermal balance could also be achieved with heat extraction reduced by more than 20% in heating requirement dominated areas.