Abstract: In order to clarify the principle of real-time acoustical holography employing a liquid surface, it is necessary to analyse the transformation from sound signal to rippled liquid-surface （i.e. hologram） and that from hologram to optical image. In this paper, a more thorough theoretical analysis of the two transformations is made by means of Fourier analysis technique. The formulas calculating the deformation caused by the "reference" sound beam and the "object" sound beam, which has arbitrary spatial distribution, is presented. Also, some calculated results of the liquid surface deformation and reconstruction image are shown, when the spatial distribution of the "object" beam is a rectangular impulse function. From these results, the factors affecting the image quality （e. g. brightness, distortion, and resolution and so on） are discussed. A comparison between the holography image and the conventional （non-holographic） image is made. Finally, some experimental results are given. The. agreement between analytical predictions and experiment results is good.