Abstract: A new method of ultrasonic wave velocity measuring by the Schlieren system is discussed. It is convenient to observe the ultrasonic wave spreading in the acoustic-optic medium. Meanwhile，an image of the periodic istribution of the refractive index can be shown on the observation screen under some circumstance，which can be used to calculate the ultrasonic wave velocity in the medium. This new method of velocity measuring helps to have a vivid understanding of the spreading of ultrasonic wave in the acoustic-optic medium.

Key words: Schlieren method, acoustic-optic diffraction, ultrasonic wave velocity measuring