In this paper, mechatronic design of a novel robotic shark for coral reef detection is presented. To obtain good maneuverability, a barycenter regulating device is designed to assist the posture adjustment of the robotic shark at low speed. Based on STAR-CCM+ software, the lift coefficients and drag coefficients of pectoral fin are calculated using overlapping grid technique. Based on Newton-Euler approach, a dynamic model with particular consideration of pectoral fins for three-dimensional motion is established. A CPG controller is used to generate rhythmic motion of each joint. Furthermore, based on the dynamic model, three-dimensional trajectory of spiral motion and swimming speed in different oscillation parameters are simulated. The results show that swimming speed of the robotic shark can be improved by increasing the amplitude and frequency or decreasing the phase difference. Also, oscillation frequency plays a more significant role. Furthermore, under the action of single pectoral fin, the robotic shark can achieve spiral motion and the turning radius is about 35.8m under the parameters set in this article.