Abstract: In order to investigate the hydrofoil propulsion method,the bionic technology of the turtle's flexible forelimbs is studied.Based on the kinematical analysis of turtle hydrofoil,the chordwise deformation characteristics,the reverse Karman vortex street shedding,and the Strouhal number of flexible hydrofoil are studied,and then it is calculated that the Strouhal number is between 0.2 and 0.45,the Reynolds number is from 3×10² to 3×10⁴.According to the viscoelastic constitutive property of turtle hydrofoil,the half-iliac bionic flexible hydrofoil is developed,and its flexible deformation as well as tissue mode are analyzed.By use of the underwater bionic experimental sample,the direct navigation and yawing performance contrast tests of bionic sample with the half-iliac flexible hydrofoil and whole-iliac rigid hydrofoil are conducted respectively. The experiments' results show that,however the propulsion efficiency of flexible hydrofoil is higher than the rigid one only moving at the high value of ω₁,the sample's acceleration when propelled by the flexible hydrofoil is higher than the rigid one all the time.And along with the increasing of ω₁,the function of flexible hydrofoil to reduce the velocity vibration of bionic sample,always exists and becomes more and more obvious.These experiments' results provide significant technical foundation for the control and manipulation study of flexible hydrofoil in the future.