Abstract: Regarding the problem of ground heat balance in cold area, a ground source heat pump system which can seasonally accumulate environmental air thermal energy was presented. The components and operation modes of the system were introduced, and the control strategy of system operation was determined through setting up the mathematic model of each system section. Based on the mathematic model and control strategy, the transient numerical simulation was carried out for an office building in Harbin. The simulation results show that the ground source heat pump system can retain thermal balance of the soil temperature field over an one year cycle. The average coefficient of performance was calculated to be 2.44. Compared with that of the coal-fired heating and air conditioning, the system energy-saving rate is 22.3%.