To verify the stator dynamics design of rotary ultrasonic motor using in-plane travelling wave and provide methods for further optimizing, a modal testing method for this type of ultrasonic motor is discussed. Firstly, the operating principle of a rotary ultrasonic motor using in-plane travelling wave is presented. Secondly, based on FEA method, the modal analysis is conducted in order to identify the features of the ultrasonic motor. By measuring axial vibration mode of disc-shaped stator, working modes of this type of ultrasonic motor are identified using laser Doppler vibrometer PSV-300-B. Experimental results show that the modal testing method is effective to identify operating modes of ultrasonic motors using in-plane bending modes and provides a convenience way for motor design and verification.