In this paper, a simplified model of the coaxial pipe type ground heat exchanger is built based on the theory of the line heat source and a design method of the coaxial pipe type heat exchanger based on the thermal response test is proposed. The method is used to obtain the complex thermal conductivity coefficient and the total thermal resistance of a borehole of a practical project in Shaoshan of Hunan Province, and the results are compared with test values. Meanwhile, the complex thermal conductivity coefficient and the total thermal resistance of another borehole of a double-U pipe in the same project is also tested and calculated for a comparison. The calculation method is proved to be applicable for the coaxial pipe type ground heat exchanger by analyzing the intrinsic relationship of the two tests with respect to the complex thermal conductivity coefficient, the total thermal resistance, the temperature difference of the heat transfer and the heat transfer rate. With this method, the complicated calculation of the thermal resistance of the inner layer of the borehole can be avoided and therefore, the calculating process is simplified. This method can be used for practical projects.