A bionic batoid model is developed and used to study how the amplitudes of the pectoral fins affect the computational models propulsive forces.The design of the bionic model is based on a detailed analysis of pectoral fins locomotion of natural batoid fishes.The pectoral fins of bionic model are made to execute the kinematics resembling the pectoral fins of a biological fish during rajiform swimming, which makes the fluid-structure interaction as similar as the biological fins.Numerical simulations are conducted at 5 different amplitude indexes from 0.08 to 0.32 with undulating frequency at f=2.2 Hz and wave number of 0.9.Kinematic and dynamic parameters are recorded in three dimensions during the simulations.The simulation results show that the swimming velocity of bionic batoid model increases with the increasing of amplitude value in general and also indicate that the outstanding steady forward swimming of bionic batoid emerges at the amplitude of 0.14 as the biological batoid choose.