To predict the performance of bubbly water ramjet propulsion,the physical processes occurring in the diffuser,mixing chamber and nozzle were analyzed.The mathematical models were obtained separately under the restrictions of certain simplifying assumptions.The bubbly nozzle flow was calculated with two-fluid model and variable step-size Runge-Kutta scheme.The influence of area ratios(mixing chamber to inlet area,Am/Ai) ,inlet area A i,air mass flow rate,vessel speed,initial bubble radii and half nozzle converging angle on the thrust and efficiency was investigated by comparing the simulation results.It is indicated that bubbly water ramjet propulsion is more effective for bigger area ratios Am/Ai and bigger inlet area Ai.With the increasing air mass flow rate and vessel speed,the thrust increases,but the efficiency decreases.The increase in half nozzle converging angle and initial bubble radii reduces the ramjet thrust and propulsion efficiency.The results are useful for further investigation of bubbly water ramjet engine.