：The propulsive mode of high-power tail-swing bionic propulsion combined of common drive (such as motors,hydraulic motors) and mechanical transmission is the most potential propulsive mode in the field of underwater automatic craft in the future. A kind of tail-swing propulsive system based on the linear hypocycloid is proposed. The system has advantages of phase difference adjustable,no quick return motion,able to achieve the integration of speed reducing and motion conversion. On the basis of propulsion performance analysis on the number of joint points and tail movement mathematical model,a black box on tail-swing propulsive system is build. Based on design conditions of motion parameters (such as tail swing propulsive parameters,joints,relations between parameters,etc),working principle and structure design of two-joint tail-swing propulsive system based on the linear hypocycloid is completed. Kinematic simulation results show that the linear tail-swing propulsive mechanism could achieve the synthesis of simple harmonic motion with adjustable phase. The feasibility of the device is verified through comparing with the sample of carp’s tail movement.