Abstract: The fundamental wave approximation is the main research method of wireless power transfer (WPT) technology. In this method, the rectifier load fundamental impedance is equivalent to a certain pure resistance, which provides a basis for system modeling and analysis. However, this method ignores the effect of rectifier load harmonic impedance, which leads to a large error between the actual response of system and the theoretical analysis result, affects the system model accuracy and limits the further optimization design of WPT system. In this paper, the WPT system based on series/series-parallel (S/SP) compensation network was taken as the research object, the reason for the error in modeling using the fundamental wave approximation was analyzed and an accurate calculation method based on the iterative method for the fundamental wave and harmonic equivalent impedance of the rectifier load was proposed. On this basis, an accurate circuit response model of the WPT system was established, which could effectively characterize the distortion characteristics of the transmitter coil current. According to the relationship between the system response and the compensation network parameters, the optimal design method of inverter switching loss was proposed. Finally, a 3kW WPT system prototype was built. The experimental results verify the correctness and feasibility of the theoretical analysis.