To study the problem of size matching of the heating tank and the thermal storage tank in the photovoltaic thermal-heat pump system, a simulation model of the photovoltaic and thermal-heat pump system was established by using TRNSYS software. The model was tested using the measured data, and the findings revealed that the errors were within reasonable bounds, indicating that the simulation model was accurate and dependable. Thermal storage tanks with the sizes of 30, 60, 90 L/m² were selected to match the heating water tanks with different capacities of 100, 200, 300 L, respectively, and an annual operating performance simulation of the system model was conducted using the system model. To evaluate the system, the annual exergy loss was chosen as the evaluation index. Simulation results show that the annual exergy loss of the system is the smallest when the capacity of the storage tank is 60 L/m² for all the three different capacities of the heating water tank. As a result, the thermal storage tank with a size of 60 L/m² is advised to match each capacity of the heating water tank.