Abstract: A geometric model of friction reduction of ultrasonic vibration based on traveling wave ultrasonic motor(TWUSM) is presented.Three driving conditions were adopted to drive the rotor of TWUSM to simulate the frictional driving characteristics of the TWUSM,which was driven by electromagnetic motor,by electromagnetic motor combining with one phase standing ultrasonic wave,and by TWUSM respectively.The experimental rig was used to simulate the friction characteristics of the TWUSM.A conception of friction coefficient reduction rate of ultrasonic vibration was introduced.Effects of the speed of electromagnetic motor,pre-load,exciting voltage and friction materials on friction coefficient of the friction couple of stator and rotor are experimentally investigated respectively.The phenomena of friction reduction in ultrasonic drive was obvious at high relative sliding speed,small pre-load,and large vibration amplitude of ultrasonic vibration.