Abstract: The test blocks with welding defects were detected by the method of metal magnetic memory, and the testing ability of the metal magnetic memory technology on welding defects including crack, porosity, incomplete penetration, lack of fusion, slag inclusion was studied. For the welding defects such as cracking, porosity, incomplete penetration, lack of fusion, slag inclusion in welded joints, their average value H_ave and the maximum value H_max of the magnetic field intensity, the area surrounded by the magnetic field intensity curve, the average value and maximum value of the magnetic field intensity gradient, the area surrounded by the magnetic field intensity gradient curve, were calculated and analyzed, respectively, which is also compared with the defect-free regions. The results show that、 of the welding defect are significantly different from parameters of the defect-free regions, whichcan accurately identify the location of welding defects. Whether it is a welding defect, or welding residual stress, itcan lead to changes of magnetic memory signal, but there are essential distinction between above two.