Abstract: An underwater turbine engine propulsion system has the particularities of its structure characteristic and working condition.Mathematical modeling of the engine propulsion system is necessary for the system analysis and system design. Combining the physical mechanism analysis and characteristic data fitting of primary components,a mathematical model of propulsion system of underwater turbine engine system with open loop cycle is built in this paper.The model has simple structure,clear physical meaning and high calculating precision.And its parameters adjustment,program coding and calculation are convenient.The model can be used for performance evaluation and optimization design of the propulsion system.As the model describes the dynamic process of the system,it is the base of the design of the engine control system.