Propulsion efficiency is the core point of underwater vehicle，which produces effects on the practical application of machine equipment． In this paper，through kinematic character of the thunniform mode fish with undulatory movement，the fish robot was developed as a multi-rigid body system which could be divided into body，pectoral fin and caudal fin，combined with the external force of fish robot，the dynamic model was established with Newton-Euler method． Based on this dynamic model，with the goal of propulsion efficiency，the genetic algorithm was selected to optimize the kinematic parameters． By optimizing the multi-body coordination between fish body， tail fin and pectoral fin，the propulsion efficiency of the robot fish was improved． In connection with optimization results，the kinematics numerical simulation of robotic fish was further carried out． The results showed that at the speed of 1. 415 times of the body length，the efficiency of the robot-fish was 49. 9% ．