The development of ground source heat pump system (GSHP) is hindered by some factors such as high initial investment, difficult construction process of ground heat exchangers (GHEs) and imbalanced underground heat transfer. The heat transfer model of the GHEs is very complicated, and so many influential parameters are involved. The length of the buried pipe cannot be calculated by manual calculation. Accordingly, this paper mainly introduces the optimization design method of the hybrid GHSP system with the auxiliary gas source boiler, and the special software including software interface, internal algorithms and result analysis is developed. Both the practicality of hybrid ground source heat pump system with gas boiler and the reliability of the design simulation software are verified by the actual project. The results demonstrate that the gas boilers can effectively reduce the peak-load of the GHE, and therefore reduce the designed length of the buried pipe, solve the problem of underground thermal imbalance and improve the efficiency of the unit. Meanwhile, the software can simulate the operating conditions of the composite system for a long time, which can provide both theoretical support and technical guidance for both research and engineering application of the hybrid GSHP system in the future.