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The interface contact model between the stator and the rotor of traveling wave ultrasonic motor is presented, assuming that the rigid stator contacts the flexible rotor over an area, and the frictional material is regarded as distributed linear spring and without shearing deformation, from which the mechanical characteristic of the motor and the interface transmission efficiency are derived. And then the effects of the motor’s parameters on its performance are investigated, which will be helpful to the design of the ultrasonic motor.