This paper presents the mechanical design, kinematic modeling and simulation of a robotic dolphin. The mechanical structure of robotic dolphin was designed according to the bionics. The motion equation of the robotic dolphin was established by reference to the motion equation of submarine. Then, the motion simulation of the sinusoidal movement mechanism and the caudal fin was achieved using SolidWorks. The motion equation of the robotic dolphin was the basis of the robotic dolphin's motion control. The analysis results of motion simulation confirmed the effectiveness of the robotic dolphin in propulsion.