Abstract: A series of friction materials with different thickness for traveling wave ultrasonic motor (TWUSM) were developed. The effects of the thickness of the friction material on the un load speed and stalling torque of TWUSM were investigated with a simulated tester of TWUSM.A simple contact model with friction between the stator and rotor of a TWUSM was established. The variations of the contact state between the stator and rotor with the thickness of the friction material were simulated numerically using finite element method based on the contact model. The range of thickness of friction material with suitable contact deformation between the stator and the rotor was presented. It has been found that the optimum thickness of the friction material for TWUSM can be determined conveniently based on the method established, by taking into account the requirement for suitable contact deformation of the stator and rotor. Appropriate out put performance of the ultrasonic motor is attainable at a thickness of 0.3 mm of the friction material, while un stability and processing difficulty are caused when the thickness of the friction material is too small.