In order to obtain the effect of roughness on aerodynamic performance of airfoil, the Computational Fluid Dynamics (CDF) numerical simulation is used to study the aerodynamic performance of S809 airfoil when the airfoil layout roughness, and the sensitive roughness was obtained.The airfoil lift and drag changes were simulated when the airfoil suction surface and pressure surface were roughness sectionally arranged. The symmetrical thickening method was used to treat the S809 airfoil. The blunt trailing edge was modified, and the optimal trim and aerodynamic performance of the original airfoil were compared.The results show that 0.5 mm roughness is the sensitive roughness of S809. The suction surface is 5%, 55% chord length is 45% and pressure surface is 65% chord length is the sensitive position of airfoil roughness. 2% chord length of blunt tail modification is the optimal one, and the lift of modified airfoil is obviously increased after layout roughness. The comprehensive index number shows that the modified airfoil phase is improved. Compared with the original airfoil, it has relatively low roughness sensitivity.