Ground source heat pump system can achieve high efficiency of performance by utilizing annually constant underground temperature to provide heat source for space heating and cooling. Generally, the depth of constant-temperature zone under the ground depends on surface heat flux and soil properties. The deeper the ground heat exchanger is installed, the higher the heat exchange rate can be acquired. However, in order to optimally design the system, it is necessary to consider both the installation cost and the system performance. In this study, performance analysis of ground source heat pump system according to the depth has been conducted through the case study.