This paper studies the effect of the the caudal fin superimposed chordwise deformation on the propulsion performance. The calculation results show that the appropriate chord deformation of the caudal fin can effectively increase the propulsion efficiency. It describes the shape change of dolphin tail by mathematical formula, and studies the propulsion performance of dolphin tail by numerical method combined with morphing mesh technology. The quasi-propulsive efficiency is used to evaluate the propulsive efficiency of self-propelled objects. The results show that the active deformation of the caudal fin can effectively increase the propulsive efficiency and provide a theoretical basis for the design of the flapping bionic propeller.