Abstract: As marine speed reducer can＇t insure an agreeable matching when both the engine and propeller operate under high power conditions,the approach that incorporates a new concept of impulse stepless gearbox as the subst itute for the marine speed reducer was proposed to implement the operation with constant power variable speed.The various aspects concerning the basic structure of the new impulse stepless gearbox,including the method for self-locking and unlocking of face contact overrunning clutch,as well as calculations on the operation efficiency and service life of the gearbox were introduced.The issue of complete equilibrium for the new impulse stepless gearbox was also discussed.The analysis shows that using this gearbox will result in the desired performance and allows for the engine and propeller operate under high power conditions simultaneously,and rep lacing the speed reducer by the impulse stepless gearbox is feasible.