Abstract: To avoid cavitation of a propeller at high rotational velocity, high speed surface ships incline to use water jet propulsion systems. This study is inspired by the conversion of heat into power in high temperature and high pressure gas driving a piston. According to the principles of plug flows, a novel pulse water jet propulsion system is presented with low costs and simple construction, and the model of the water jet propulsion system is established. According to this model, theoretical calculations and numerical simulations are conducted in the expansion process. With the simulation results, the parameters of the model are optimized, thus the relevant parameters which are closer to real working conditions, such as propulsive force and total impulse, are obtained. Calculation results verify the reasonability of the proposed model.