Abstract: A bionic fish mimicking Cownose Ray is constructed to realize the similar motion of fishes swimming by oscillating pectoral fins. Firstly, a principle model of the bionic pectoral fin which combines the active and passive composite flexible deformation abilities is initially proposed based on biological properties and motion laws of oscillating pectoral fins. Then, the design feasibility is verified by kinematics simulation with ADAMS, and a bionic prototype is fabricated. The free swimming tests show that the prototype has a maximum velocity of about 0.46 m/s (or 1 body length per second). What's more, the bionic fish has the pivot turning ability and the maximum turning speed is up to 60° per second. Compared with other similar robotic fishes at home and abroad, the bionic fish in this paper performs distinct advantages both at velocity and maneuverability. Based on the quasi-steady blade element theory, a simplified hydrodynamic model of the bionic pectoral fin is proposed. Then, a hydrodynamic experimental platform is built to evaluate the effectiveness of the model, and some other experiments are carried out to further study the hydrodynamic characteristics of the bionic pectoral fin. The experimental results show that the bionic pectoral fin can produce periodically changed thrust and lift forces, which are bound up with the kinematic control parameters.