The unmanned underwater vehicle hybrid propulsion system exploits the exothermic reaction between aluminum and water which will produce high temperature, pressure steam and hydrogen mixture that can be used to drive turbine to generate power. The research shows that this system has high energy density. Three new system configurations corresponding to different working cycles were investigated respectively, and their performance parameters in terms of net power, energy density and global efficiency were discussed. The results of the simulation show that the reaction between the direct return of high temperature steam and the aluminum enhances the temperature of steam, and the system's performance is reduced. An evaporator component and a solid heat exchanger are added into system in order to make full use of the solid product heat, and so the system performance is improved. The addition of double combustion chamber and wall cooling structure avoid the design of the high temperature compressor component on one hand, and solve the thermal protection of the combustion chamber on the other hand, which brings the improvement of the system performance. The results can provide useful information for the overall design of the unmanned underwater vehicle hybrid propulsion system.