Abstract: The mechanism of magnetic memory effect on ferromagnetic material under loading was studied. By fracture mechanism and dislocation theory, the polymerization model of magnetic domain wall was presented on the basis of the analysis of microstructure changes. The oriented magnetization of specimen was viewed also, and then the magnetic flux leakage of specimen in the stress concentration area or microstructure damage area through magnetic dipole model was calculated. Results showed that, magnetic changes in the stress concentration area or microstructure damage area could be explained by polymerization model of magnetic domain wall.