In order to describe the acoustic wave quantitatively induced by laser breakdown, an improved method for computing underwater acoustic wave induced by laser breakdown is presented based on model of point source. Acoustic wave induced by laser breakdown with single and multiple regions is computed based on wave equation and underwater explosion theory. The characteristic of acoustic signal such as pressure waveform, sound source level, transmitting and directivity is analyzed quantitatively, and it is verified through the experiment data contrast. The results show that the coincidence between the computed and experimental data validates the theoretical model. As the laser energy increases from 0.1 J to 0.8 J, the sound source level increases from 182.4 dB to 188.2 dB, but when the laser energy exceeds 0.3 J, sound source changes slightly. The power of acoustic signal is highest in vertical direction of cylindrical region of plasma, and lowest in parallel direction. The intensity of acoustic wave makes an inverse proportion to the square of distance in all directions.