According to the large stiffness and small deformation for bionic fish with isotropic materials as substrates, the problem of vibration behavior is studied on the elasticity modulus of the substrate material for the influence of the flexible composite bionic fish tail. First, a flexible bionic fish tail structure driven by a macro fiber composite(MFC) is designed. Then, based on substrates with the same values of poisson ratio and density and different elastic moduli, the tail′s vibration is simulated with COMSOL software, and the extreme value between tail swing displacement and the elastic modulus is obtained. Further, when compared with the elastic modulus of the isotropic material, the anisotropic material is suitable for the substrate material. Finally, the flexible tail is completed with anisotropic substrate materials manufactured with MFC. The feasibility of the design and the rationality of the mathematical model are verified with experimental measurements of the vibration performance.