Abstract: Firstly, a simple linear CPG (central pattern generator) model is adopted to implement smooth transformations between various swimming gaits. Then, a function of the transition layer between CPG control parameters and the speed as well as the turning velocity of the robotic fish can be obtained through experiments. Further, an improved posture controller based on the proportional guidance controller is proposed, in which the posture error of robotic fish is redefined and its angle error is added to the proportional controller of the position error as a bias compensation. The feasibility and effectiveness of the proposed controller is verified by various experiments.