Its main component is a cylinder with bigger diameter and smaller length which is revolved by transmitting machinery. Materials are put in cylinder through the feed opening and then thoroughly grinded. The falling course of iron balls and ores can produce huge falling impact and autogenous grinding. The continuous feeding of ores can create considerable pressure to make ores move from feed opening toward discharge opening. Finally, acceptable particles are discharged from the discharge opening. Acceptable ore particles are carried away by water by wet mill, or by air by dry mill. The hollow shaft comprises reciprocal screw impellers that can carry overflowed iron balls and coarse ores back to mill. Energy-saving overflow ball mill has simple structure and higher operation rate. Equipped with rolling bearings, it can considerably save energy.