The hypothesis that contact surfaces of stators and rotors are smooth is used in the contact model of ultrasonic motors, but the actual contact sur faces are rough. Now it is lack of survey on the contact state of the stator and rotor. As a result, firstly the deformation law of the friction layer on the st ator surface of a travelling wave ultrasonic motor under prepressures was stud i ed by tests. Secondly, the change law of the natural frequency, amplitude and ve locity of the stator vibration with the preload was investigated by a PSV300 FB laser vibration meter. Finally, the contact interface properties between the sta tor and the rotor were analyzed by using the electrical contact method. Experime ntal results show that the vibration amplitude of the free stator (not be couple d with rotors) is of the same order of magnitude as the deformation of the frict ion layer under the preload of 100N, and the stator and the rotor never separa t e during running. The study indicates that traditional contact models can n ot reflect the actual contact performance of the stator and the rotor.