Abstract: The types of surface scratches on the inner surface of hole drilled with PCD tools are analyzed, as well as the reasons of their appearance to eliminate them. Experiments are implemented to test the effect of methods such as optimizing the main principal deflection angle and adding spray. Results show that in rough machining, there formed an aluminum ring chip in the hole. Then the ring chip, driven by the fine machining tool, would scratch the hole surface. It is also found that optimizing the main principal deflection angle of the edge of coarse machining tool, thus from 85° to 48°, could reduce the ring thickness and limit its appearance. Actual production proves that this method could eliminate the remaining aluminum ring in finished product and thus improve the surface quality of inner hole.