Abstract: The stepless-speed control for operating performance of thermal propulsion system is a key technology to increase torpedo range and hitting probability. This paper establishes mathematical models of main parts through analyzing torpedo′s thermal engine and propeller, and presents a stepless-speed control scheme with close-loop mode for swashplate piston engine with variable fuel pump. The control laws are obtained for computer simulation using variable structure control method. The algorithm of integrated control laws achieves easier computation for engine control unit(ECU). Simulation results show that the speed error meets the requirements of engine system under the preset angle of torpedo trajectory and the transition process of changing speed. The control laws can eliminate the vibration of system and has good performance of tracking engine speed.