To improve the transmission efficiency of resonant wireless power transfer system in high frequency condition, the class E power amplifier is used as a driving source based on the traditional structure of wireless power transfer system. An adjustment method of load network for class E power amplifier in wireless power transmission system is proposed to further reduce the system losses, and then, the optimal matching parameters of load network in soft switching condition are calculated. The effect of load network changes on the system efficiency and the state of soft switching by adjusting the duty cycle of the switch are verified. Result shows that the system output power can get 78 W at 1 MHz frequency, and the system power efficiency is up to 76.5％.