Abstract: In order to test and verify the radiation surface vibration of Class Ⅲ flextensional transducer in working state, Doppler laser vibrometer is used to measure the vibration modes of Class Ⅲ flextensional transducer, and then the measuring result is compared with the simulation result of finite element software. The measurement shows that the resonant frequency of the first-order vibration mode of transducer shell is 1 729 Hz, and the resonant frequency of the first-order vibration mode of transducer is 2 065 Hz. They are closed to the simulation results. Research results show that Doppler laser vibrometer could be well used for measuring transducer vibration mode and for transducer aided design.