The objective of investigation is to use numerical simulation obtain the effect of three different flexible deformation parameters (the maximum deforming amplitude, the phase difference between the plunging motion and the deformation motion and location of the maximum deforming) on unsteady aerodynamic performance of an airfoil with plunging and pitching motion. It is shown the effect of flexible deformation at low Reynolds number is obvious. The effect of the maximum deforming amplitude and the phase difference on aerodynamic forces is quite significant while the time courses of CL and CT don’t almost change with location of the maximum deforming. Different deforming amplitude and the phase difference may be advantageous or disadvantageous for averaged aerodynamic forces. Larger phase difference can produce more thrust and make the forward flight faster. Compared with the rigid airfoil, the appreciate combination of deformation parameters is beneficial in MAV design.