Abstract: The stable and clear diffraction patterns were obtained by an experiment of laser diffraction from 1-D liquid surface acoustic wave (SAW) excited at low frequencies. When the incident direction of laser and the propagation direction of SAW are in same plane, it is observed that the distribution direction of the diffraction patterns is also located in this plane. However, when the incident direction of laser and the propagation direction of SAW are not in same plane, the distribution direction of the diffraction patterns is not located in the plane with the incident light. The formula of laser diffraction from one-dimensional SAW in oblique incidence was theoretically derived by the aid of the establishment of the proper coordinate system. Furthermore, the relation between the distribution direction of the diffraction pattern and the incidence angle of the laser was also achieved. The wavelength of SAW was obtained by the calculation of the data from the experiment and it agrees with the results obtained by the other methods.