The building energy consumption per unit area continuously decreases in recent years so that the ground-coupled heat pump system (GCHPS) with the horizontal ground heat exchanger (HGHE) no longer requires excessive underground area when they are applied to buildings. This phenomenon contributes to the popularity of the horizontal GCHPS. In this context, a simulation model of the horizontal GCHPS is developed to investigate their main design factors from the economic point of view. Taking the annual cost of GCHPS as the evaluation index, the orthogonal experiment design (OED) method and the analysis of variance (ANOVA) are applied to determine the influence degree of each factor on the economic aspects of the GCHPS. Then the control variable method is employed to analyze the effect of each factor on the performance and the economy of the GCHPS. The results of the present study show that the main affecting factors of the problem are the pipe length, pipe spacing, buried depth and pipe diameter of HGHE. Moreover, it is found that the flow rate of the heating medium has negligible impact on the HGHE. It is concluded that these factors in the order of importance are the pipe spacing, pipe diameter, pipe length, buried depth of the HGHE and the flow rate of the heating medium. Increasing the aforementioned parameters in accordance with the order of significance can improve the performance and reduce the operational expense of the horizontal GCHPS, but it increases the overall cost of the system.