Abstract: This paper analyzes the feasibility of applying several smart materials to bionic fish muscle.A four-joint flexible underwater pisciform propulsion system is developed and the control flow chart is presented.Then a kinematics equation is set up,and a deep analysis on unsteady swimming phenomenon of the propulsion system as well as the cause of this unsteadiness are given.Meanwhile,several ways are proposed to improve stability.Tests are made to verify whether the symmetrical leading surface and the additional fin as well as the location of the fin base have any influence on stability of the system.Finally,comparative experiments prove that this design is feasible for improving swimming stability of flexible multi-joint underwater pisciform propulsion system.