Abstract: The free fall of plates is a classic problem of fluid mechanics-dynamics coupling, which has obvious nonlinear characteristics. According to the nonlinear characteristics of 2D freely falling plates, the equations of motion coupled with the Navier-Stokes equations were numerically solved in this paper. The motion states and trajectories of freely falling plates at different initial angles were compared, and characteristics of the nonlinear system were studied with phase trajectories and spectrum analysis method. The research results indicate that there are differences on motion states and trajectories with different initial angles in initial stage of free fall, and these motions are non-regular fluttering and small-amplitude tumbling. However, the motions finally turn into periodic fluttering or tumbling in later stage of free fall. The initial angle has little effect on the motion mode.