Abstract: In order to analyze the intensity and position of the diffraction pattern from the liquid surface wave,a low-frequency signal generator was used to produce a sinusoidal output at low frequency,which was then used to drive the surface acoustic wave(SAW)exciter.A laser beam was directly incident upon the water surface where the SAW was excited and diffracted.Thus,a technique for low-frequency SAW visualization was developed based on the light diffration.The intensity curve was draun and the intensity and position of each-order diffraction spots were obtained.The asymmetrical position and intensity were also discovered.The dependence of the diffraction intensity on the liquid surface waves was theoretically derived.The approximate conditions of the surface wave diffraction and the half angular width were analyzed,respectively.When laser was at normal incidence,the symmetrical distribution was theoretically derived.The theoretical and experimental results are in good agreement.