A flow control method using a small plate in front of the leading edge of a   NACA0012 airfoil to achieve good aerodynamic performance is proposed. Effectiveness of  the proposed method is numerically studied by using a self-developed CFD program called  UCFD. At a certain angle of attack, including of parameters including length, initial installation  angle and installation position of the plate on the control of flow separation over  the airfoil are investigated. The optimal length, initial installation angle and installation  position of the small plate are obtained with an orthogonal optimization method that aims  at maximizing the lift-to-drag ratio. Numerical results suggest that this passive flow control   method can efficiently suppress flow separation.