Contact and friction model of ultrasonic motors is of great importance for structure design and performance optimization. In order to describe the contact and friction problems of a ring type standing wave ultrasonic motor, a contact and friction model of the stator and rotor is proposed based on the coulomb friction law with viscous friction. The variation of frictional force on the contact surface in one vibration cycle is investigated based on the proposed model. The impacts of different radial vibration amplitudes and structural parameters of the stator on the performances of the motor are analyzed. Finally, torquespeed characteristics of the motor are measured. The experimental values are compared with the calculated values, and the good agreements are obtained. In addition, the torquespeed characteristics calculated by using the model based on coulomb friction law are also compared. The comparison results show that the model based on coulomb friction law with viscous friction describes the friction drive characteristics on the contact surface more accurately than the model based on coulomb friction law.