Abstract: The main shaft bearing of a digital controlled lathe was damaged. The causes of bearing damage were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination and hardness test. The results show that early contact fatigue occured in both main shaft bearings, but the damage degree was slight. There were damage pits and furrows formed by abrasive wear on the surface of one of the bearing raceways. The abrasive particles were hard aluminum debris produced by lathe machining. The debris entered the bearing, formed extrusion pits on the contact surface and moved with the rolling body. The furrows were formed on the surface of the raceway, which increased the roughness of the contact area and eventually led to poor rotation of the bearing and abnormal noise.