Aimed at the problem of hydrodynamic for tidal current turbine,the paper used CFD numerical simulation method and took NACA0018 as reference airfoil to analyzed the change of flow field of original and wing airfoil, and the impact of flap length on dynamic characteristics and surface static pressure coefficient distribution of airfoil.Numerical results show that the flap airfoil stall angle of attack can be delayed, and after reaching the lift coefficient,the original wing stall angle corresponding to the angle of attack increased;the influence of flap on airfoil flap pressure distribution in a small angle of attack is less.When flap length is 0.3c (c the airfoil chord), the change of pressure coefficient is most evident;when the angle of attack approaches the smallest and flap length is 0.2c, the airfoil optimal hydrodynamic characteristics is optimal;after reaching the stall angle of attack,the influence of flap on wing flow field and static pressure coefficient distribution is greater.The distribution of pressure area range of airfoil suction surface is uniform.When the length is 0.2c the hydrodynamic characteristics is optimal.The lift coefficient has greater increase than that of original airfoil,but the resistance coefficient changes little.