The combined use of solar energy and ground-source heat pump system may provide a reasonable solution to the energy crisis and low utilization efficiency of single energy. Herein, a numerical model of a solar assisted hybrid ground-source heat pump (SAHGSHP) system composed of multiple types and lengths of borehole heat exchanger (BHE) array was developed. The effectiveness of this model was validated by experimental data of a SAHGSHP system located in Tongzhou, Beijing. The verified model was used to study the performance sustainability of SAHGSHP system under different seasonal operation modes and its influence on the temperature of rock and soil. It was shown that for different types of BHEs in heat extraction periods of SAHGSHP systems, the outlet temperature decline rate decreases by an average of 2.30%, the temperature decline rate of rock and soil at the reference point under single-season operation decreases by an average of 0.78%, and the temperature increase rate of rock and soil at the reference point under double-season operation increases by an average of 0.53% compared with that of hybrid ground-source heat pump (HGSHP). The results of this study could provide a further understanding for analyzing the seasonal operation mode of SAHGSHP.