Abstract: In the present research, physics of laser propulsion underwater was investigated by experiments and numerical simulation. Two physical processes of laser propulsion were observed in experiments. One is laser-matter interaction during laser irradiating propelled object, in which the laser induced plasma with short duration and high amplitude was generated. The object was propelled under the pressure of plasma. Another is bubble pulsation after the annihilation of plasma, resulting in the movement of object under bubble pressure with relative long duration. In addition, high speed of object was also observed for high impedance medium around the object and for propulsion near free surface of water. Based on the experiments, a physical model as well as simulation method were developed, by which the characteristics of laser propulsion underwater, including applied pressure and resistance histories, laser induced bubble pulsation, etc. were obtained. The simulated results agreed well with experiments, providing a valuable insight into the physics of laser propulsion underwater.