The two-dimensional incompressible N-S equations and the SST k-ω turbulence model were used to study the aerodynamic performance of a wind turbine airfoil under rough surface conditions. The DU 95-W-180 airfoil that is widely used in wind turbines was chosen as the object. The studies were mainly done as described: the lift coefficient and the drag coefficient of the airfoil under different roughness heights on full surface and different roughness tape locations were computed, the trend of the lift coefficient and the drag coefficient with the roughness height and the roughness tape location were analyzed, the critical value of the roughness height and the roughness tape location，the trends of the lift coefficient, the drag coefficient and the ratio of lift coefficient and drag coefficient with the roughness height at the critical locations were also analyzed and the results were gained.