The Aerodynamic analysis of the wind turbine airfoil at low Reynolds number is important for the airfoil research. The coupled method with boundary layer transition model and CFD method based on RANS were carried out to study the aerodynamic performance of the wind turbine airfoil S809.The comparison of free transition,forced transition and fully turbulent were performed to illuminate the influence of transition location on aerodynamic analysis of wind turbine airfoil.