The invention discloses a method and a device for measuring the speed and frequency of ultrasonic traveling wave in a liquid. The method comprises the following steps that a monochromatic parallel
light beam is vertical to an
ultrasonic transmission direction and radiates a dynamic ultrasonic
grating that the ultrasonic wave forms in the liquid; the dynamic ultrasonic
grating penetrates through a lens and the
diffraction spectrum of a traveling wave ultrasonic
phase grating is formed; the spectrum is processed and imaged through an amplitude filter and an
imaging lens, and a spectrum image of the ultrasonic traveling wave
grating is obtained; the spacing of two adjacent spectral lines on the spectrum image is measured, and the
wavelength of the ultrasonic wave in the liquid is calculated; the change of an electrical
signal after the previous level of spectrum and zero level spectrum of the spectrum image are mixed is detected or recorded, and the frequency of the ultrasonic wave is worked out; the speed of the ultrasonic wave in the liquid is worked out through the
wavelength and the frequency. The device for realizing the method comprises a
light source, a transparent sink, a lens I, the amplitude filter, the
imaging lens and the measuring device which are sequentially connected, and a sound-absorbing medium and the ultrasonic
transducer are arranged in the transparent sink and are respectively arranged on both sides.