In this study, the aerodynamic performance loss of the NACA 64618 section, which is part of the baseline wind turbine blade, due to 5 different types of surface erosion at the leading edge zone, has been evaluated using 3D numerical simulation. In order to consider the random distribution of the surface damage types in areas close to the leading edge, it is essential to simulate sections considering the depth or width of the blade element, and therefore, 3D solutions should be used, which is done here as well. The geometric pattern and dimensional range of the damages in the leading edge areas, have been classified in two separate groups, namely mild erosion and severe erosion, based on experimental data. The flow field is assumed to be incompressible and the k-ω SST turbulence model has been selected. The simulations have been performed in the range of angles of attack between -5 and 25 degrees and in 3 airfoil states: healthy, mild erosion, and severe erosion. The results of this study showed that leading edge erosion, significantly increases the drag coefficient corresponding to a given lift coefficient, which is a decrease in aerodynamic efficiency. In order to quantitatively compare the results, characteristic curves have been plotted in terms of angle of attack and lift coefficient in the three aforementioned cases. The increase in drag and the loss of efficiency are particularly greater at higher angles of attack, and the level of damage, i.e. mild or severe, significantly changes this trend. Also, among the types of erosion considered, cracks along the blade length, perpendicular to the chord, had a greater impact on performance reduction, such that the maximum lift coefficient and maximum aerodynamic efficiency decreased by 35 and 50 percent, respectively, and the drag coefficient at maximum efficiency, would be increased by 500 percent.