This study set out to investigate the performance of morphing flap on dynamic stall alleviation. The unsteady flow field around the sinusoidally oscillating NACA 0012 airfoil are simulated by computational fluid dynamics (CFD) and dynamic mesh method. Two morphing flaps are compared with the rigid plain flap in terms of control effect and energy consumption. The numerical results show that, when the pulse signal of a sinusoidal shape is used, the flap deflection may be delay the formation of leading-edge vortex (LEV) and accelerate the development of the trailing-edge vortex (TEV). Meanwhile, the peak value of pressure distribution on the trailing-edge is reduced, and the large negative pitching moments are also decreased. The 2nd order morphing flap proposed in this paper could reduce the large negative pitching moment with the least energy requirement.