The active torsion propulsion mode of a caudal fin,composed of macro fiber composites(MFC)and carbon fiber orthotropic composite material is proposed.The caudal fin is excited by the piezoelectric structure to vibrate flexibly.The work principle is firstly analyzed by finite element method(FEM)and experiments.Then the caudal fin is optimized to increase the torque and improve the streamline,and the added mass effect from the water is discussed in terms of the frequency of the structure.The torsion resonance frequency is around 103 Hz in the air and decreased by 75%to 25 Hz in the water.Finally,the mean thrust is discussed and measured to be 11 mN at900V(Peak to peak)driving voltage.A flexible micro robot is developed and tested.The locomotion velocity and flow velocity is 320mm/s and 268mm/s,respectively.The results of the simulation and experiments indicate that the locomotion of the biomimetic aquatic robot has fast movement characteristics. The active torsion propulsion mode of a caudal fin composed of macro fiber composites (MFC) and carbon fiber orthotropic composite material is proposed. The caudal fin is excited by the piezoelectric structure to vibrate flexibly. The work principle is well documented by finite element method (FEM) and experiments. Chen the caudal fin is optimized to increase the torque and improve the streamline, and the added mass effect from the water is discussed in terms of the frequency of the structure. Torsion resonance frequency is around 103 Hz in the air and decreased by 75% to 25 Hz in the water .Finally, the mean thrust is discussed and measured to be 11 mN at900V (Peak to peak) driving voltage. A flexible micro robot is developed and tested.The locomotion velocity and flow velocity are 320mm / s and 268mm / s, respectively. The results of the simulation and experiments indicate that the locomotion of the biomimetic aquatic robot has fast movement characteristics.