A swimming mechanism for frog inspired robot is designed. Firstly, the prototype of the frog inspired robot is designed through analyzing the biological structure of real frogs. Pneumatic muscles are selected as the drivers to drive the rotational motions of hip, knee and ankle joints. The knee driving muscle is positioned on the body, driving the knee joint through steel wires, and therefore, the leg mass is reduced. Then the kinematics model of the robot system is established and analyzed. The forces exerted on the frog are analyzed and introduced into simulation environment in ADAMS, so the water environment is simulated and the dynamic analysis is conducted. The underwater swimming experiments of the frog swimming robot are carried out, and average velocity in propulsive phase is 339mm/s. Through the comparative analyses of the two different methods, by dynamics simulation and prototype experiments, the motion patterns of the robotic hindlimb are basically the same. Accordingly, the feasibility of the designed frog inspired swimming robot can be verified.