In order to research the bionic mechanics in unsteady flow,a two-degree of freedom(DoF) motion model was established for a rigid pectoral fin,and the experimental device named imitating pectoral fin system for the propulsive system was developed.This fin propulsive system consists of two servomotors and can realize various demanded feathering lead-lag coupling motions within the system limitation.During the experiment,the effects of phase difference,oscillating frequency,oscillating amplitudes and angular bias on the hydrodynamic performances were studied.The hydrodynamic coefficients against time in a cycle were obtained and analyzed.The study provides a foundation for the development of small underwater bio-robot.