This paper applies Co-flow Jet (CFJ) active flow control (AFC) to the wind turbine S809 airfoil to optimize the CFJ-S809 airfoil with significant lift coefficient increase at low energy expenditure. The effects of injection slot-size, injection slot location, suction slot-size and suction slot location are studied. The high fidelity in-house CFD code FASIP with two-equation k-ω shear stress transport (SST) turbulence model is utilized to better predict flow separation. The 2D Unsteady Reynolds averaged Navier-Stokes (URANS) equations are used for high angle of attack simulations to accurately capture flow unsteadiness. Steady state RANS is used for low angle of attack simulations. The baseline S809 airfoil is validated with experiment. The predicted lift coefficient (CL ) and drag coefficient (CD ) achieve a good agreement with experiment except a slight deviation at very high or very low angle of attack (AoA) due to flow separation. The predicted airfoil surface pressure coefficient distribution (Cp ) at various AoA also agrees well with experiment. The CFJ-S809 airfoil is simulated with three injection total pressure of 1.01, 1.02 and 1.03 (P tinj, normalized by free-stream static pressure), which corresponds to the Cµ varying from 0.02 to 0.09. A small P tinj of 1.01 is able to increase CLmax over 45%. The suction location study indicates that suction slot located at the geometry inflection point at 53%C is the optimum due to it’s efficiency and effectiveness to suppress airfoil stall at high AoA. The suction slot-size of 1.0%C is adopted since it decelerates the flow well with little flow separation inside the suction duct. For the injection slot-size, the 0.75%C slot-size minimizes the power coefficients by reducing the required injection total pressure, and therefore is the optimum. The injection location of 3%C is the optimum due to it’s better energy efficiency at high angle attack. Compared with the baseline S809 airfoil, the optimum configuration is able to increase CLmax by 42.3% with a similar amount or higher (CL /CD )c .