Abstract: Based on the figure of merit, the numerical simulation for the suction control of flow past an airfoil NACA0012 is conducted at Reynolds number Re=10⁴, angle of attack α=6° with the control beginning from the separation point. The effects of variations of the control area and suction coefficient on the control cost and lift-drag ratio are discussed. The results show that the lift and lift-drag ratio coefficients increase with the increase of the suction area. However, for the drag coefficient, there is only one control area which makes it minimum. For the same control area, there is an optimal suction coefficient which makes the lift-drag coefficient maximum. If the suction area size is constant, the suction coefficient should be as small as possible to get the utmost control gain. Furthermore, there is also an optimal control area which makes the control gain maximum.