The use of supercapacitors as energy storage devices in wireless power transfer (WPT) systems can significantly increase the charging speed. However, there is the problem of system transmission efficiency degradation due to the change of equivalent load impedance in the WPT system. The fuzzy PID algorithm is used to control the DC/DC duty cycle of the secondary side to realize the maximum efficiency tracking, which significantly improves the transmission efficiency compared with that of the traditional PID algorithm. First, the equivalent load impedance as a function of the system transmission efficiency in the LCC-S compensation topology is derived from circuit theory. Then, on this basis, the fuzzy control theory is utilized to regulate the output impedance of the system by controlling the DC/DC duty cycle of the secondary side to achieve maximum efficiency tracking. Finally, the simulation platform is built by MATLAB/Simulink for verification, which proves that the wireless power transmission system using fuzzy PID algorithm can realize the maximum efficiency tracking, and its maximum transmission efficiency can reach 93.10%, and the average transmission efficiency can reach more than 85%, which can realize the maximum efficiency tracking of WPT.