Abstract: The experimental system for laser -induced acoustic signals had been built for research on characteristic of laser-induced plasma acoustic signals. Acoustic signals were produced by pulsed laser focusing into water. A hydrophone was used to receive the acoustic signals. A high speed camera was used to record the breakdown procession. Time and frequency domain of laser-induced plasma acoustic signals were studied. Its directivity and transmission characteristic were analyzed theoretically, and proven by experiment. The results are as follows: The pulse width of laser-induced plasma acoustic signals is about 20 s, its frequency width is 500 kHz and main frequency is 70 kHz. It transmits in all directions and decreases proportionally to 1/r, main frequency decreases as distance increases.