Abstract: Based on the Kirchhoff law, the S-parameters, the transmission efficiency and the frequency division of the three-coil WPT system are analyzed. The phenomenon of frequency splitting is that the over-coupling between the coils causes the system to appear more than one resonant frequency. The frequency splitting occurs only in the over-coupled region. Since the internal impedance of the over-coupling region does not match the input impedance of the system, the frequency splitting phenomenon is proposed. Therefore, an impedance matching method is proposed to suppress the frequency splitting phenomenon. By adding an L-shaped impedance matching network at the transmitter and forming a conceptual impedance matching network at the receiving end, the purpose of suppressing the frequency splitting and increasing the efficiency of the system is realized. Finally, the correctness of the proposed method is compared by experiment and simulation.