In the process of rotary ultrasonic machining，the change of load will cause amplitude attenuation， which will lead to the decrease of machining accuracy and efficiency. In this paper， in order to solve the problem of amplitude attenuation in the machining process of the rotary ultrasonic machining system with non-contact power supply， the influence of load on the electrical parameters of ultrasonic oscillator is obtained through static loading experiment. On the basis of the static loading experiment， the loading experiment of the non-contact energy transmission system of ultrasonic oscillator is carried out， and the effect of load on energy transmission characteristics is obtained. The results show that the electrical parameters of the ultrasonic oscillator are changed by the combined influence of the load force， the direction of the load force and the characteristics of the machined materials.Change of the electrical parameters of the ultrasonic oscillator leads to the change of the output power of the ultrasonic system with non-contact power supply， which leads to the problem of amplitude attenuation.In this paper， the circuit compensation method of main side series capacitor and secondary side parallel capacitor is adopted to reduce the amplitude attenuation. The research results of this paper provide an experimental basis for solving the problem of amplitude attenuation.