Abstract: A two way fluid-structure interaction method is employed to simulate the aerodynamic performance and the structural response of NACA0012 airfoils, with three flexible structures on a portion of the upper surface extending from 5% to 95% of the chord from the leading edge. The impact of the elastic modulus is analyzed. It is indicated that at a large angle of attack the deformation of the flexible surface affects the unsteady flow field around the airfoil, delays the stall and improves the lift coefficient. Even when the stall occurs, the lift coefficient of the flexible airfoil decreases more slowly with the increase of the angle of attack than that of a rigid airfoil. The flexible airfoil with smaller elastic modulus has better aerodynamic performance. But too small elastic modulus is not conducive to the enhancement of the aerodynamic performance and the flexible surfaces will experience a large amplitude vibration.