Abstract: The evolution of subsurface temperature fields during ground source heat pump (GSHP) operation is governed by coupled heat conduction and groundwater advection. To address the limitations of general-purpose commercial software in computational efficiency and engineering adaptability, a three-dimensional heat diffusion-advection numerical simulation platform for GSHP applications is developed. Based on the MATLAB environment, the finite difference method(FDM) is used to discretize the governing equations. It realizes model parameter configuration, calculation control and result visualization through a graphical user interface, and supports three-dimensional simulation, cross-section analysis and data export of subsurface temperature fields under multi-heat-source conditions. The numerical stability and accuracy of the model are verified by synthetic test cases under ideal conditions. On this basis, measured geothermal and geological data from Xiamen are adopted for practical application analysis to simulate the evolution characteristics of subsurface temperature fields during short-term GSHP operation. The results show that the platform can reasonably characterize the subsurface thermal diffusion and heat accumulation processes, and can be applied to the operational analysis of GSHP systems and research on shallow geothermal energy exploitation.