Abstract: As a new method to generate underwater wave, laser-acoustics has a variety of commercial and oceanographic applications due to its merits such as high acoustic intensity, spike pulse and wide frequency spectrum. The primary model for laser-acoustic signal characteristic was established according to the linear and nonlinear theories of the laser-acoustic pulse. The characteristic that the laser may create acoustic wave in water was investigated. The research indicates that the increase of laser intensity can improve the laser-acoustic conversion efficiency in the state of the thermal expansion excitation, and when the intensity is higher than the breakdown threshold, the excitation mechanism of the laser-acoustics becomes nonlinear light breakdown mechanism. The laser-acoustics features high distance resolution and anti-interference. It has a great application prospect in underwater and airborne target detection.