Generally the underwater bio-robots take the tail fin as propulsor,and combined with pectoral fin they can manoeuvre agilely and control their position and movement at will.In nature,a lot of fishes realize to suspend itself in water to go forward and to move back up by the pectoral fin moving complexly.So that it is significant theoretically and valuable for practical application to investigate the propulsive principle and hydrodynamic performance of pectoral fin,and find the method utilizing the pectoral fin to manoeuvre the underwater bio-robot agilely.In this paper,a two degree of freedom(DoF)motion model is established for a rigid pectoral fin,and the hydrodynamic performances of the pectoral fin are studied by use of the pectoral fin propulsive experimental platform developed by Harbin Engineering University,simultaneously the hydrodynamic performance of the pectoral fin is analyzed when some parameters change.Then,through the secondary development of FLUENT(CFD code)software,the hydrodynamic performances of rigid pectoral fin in viscous flows are calculated and the results are compared with the latest experimental results.The research in this paper will provide the theoretical reference for the design of the manoeuvring system imitating pectoral fin,at the same time will become the foundation for the development of the small underwater bio-robot.