Wireless Power Transfer (WPT) technology is widely used in consumer electronics, electric vehicles and other products. The harmonics generated in the system power conversion process make the system time-domain analysis more complicated and affect the soft-switching performance of switching devices. Firstly, based on the S/SP wireless power transfer system, this paper analyzes the influence of the inverter output harmonic on the soft switch. Then, combined with the influence of the S/SP compensation capacitor parameters variation on the input impedance and output voltage gain of the system, the realization method of zero voltage switch (ZVS) for inverters in a wide load range by changing the compensation capacitor parameters is analyzed. Finally, a 6.3 kW WPT system prototype is built in this paper. Through prototype experiments, the compensation capacitor parameters on the system output voltage gain and the switch device ZVS realization have verified the correctness and feasibility of the influence analysis.