In order to reveal the anisotropic behavior of the unidirectional carbon fiber reinforced plastics (UD-CFRP) delamination during the drilling, the shape and size of the delamination on the top layer of the hole exit are investigated. The results indicated that the shape of the UD-CFRP delamination was suborbicular rather than smooth elliptical. The size of the delamination decreased with increasing the spindle speed, and the most obvious was in the direction of principal stiffness, but the max decrement was only 0.14 mm. Large area of the fiber bundle tears would easy to occur in the direction of principal stiffness with increasing the feed speed. And the size increased with increasing of the feed speed, the most obvious was also in the direction of principal stiffness, the max decrement was 0.81 mm. The shape of the delamination appeared suddenly change in the direction of principal stiffness due to the large area of the fiber bundle tears.