A laser interference technique for measuring liquid surface acoustic wave at a few tens Hertz was designed and the high visibility and modulated interference fringes, which are formed by the reflective light beam from the liquid surface, were obtained experimentally. The interference fringes are confined in a certain space range and the double brightest spots locate at the both extreme positions of this range. An analytic intensity expression of the light from the liquid surface, the angle space of the interference fringes and the angle width of the interference fringe range with the surface acoustic wave were derived theoretically. The results show that the theory predication is well consistent with experimental data. Moreover, a practical technique can be developed, based on the discovery, to measure the properties of the surface wave at these frequencies and the dynamic surface tension.