Abstract: Metal magnetic memory testing technique is one of non-destructive testing technologies grown in recent years,widely used in the fields of non-destructive testing with its many advantages; technical feature of metal magnetic memory testing is presented in the paper. Detections were carried out on the vibrating screen in Majiliang coal preparation plant with the EMS-2003 metal magnetic memory testing and eddy current testing apparatus,then an early crack with the length of 100 mm was found,which won the time for the booking of spare parts and its maintenance and avoided great economic loss likely resulted in by the founded failure. The results have important reference significance and value to detection of early defects in the other ferromagnetic constructions.