To decrease the free energy, ferromagnetic crystal would reduce the stress energy by changing its magnetic state. Under the influence of stress-induced magnetic anisotropy in the interactions of stress and geomagnetic field, the physical mechanism of magnetic memory effect is studied. Crack propagation tests are performed on plate specimens of 45 quenched and tempered steel and non-quenched and tempered steel specimen. By three-point bending fatigue experiment and measurement in situ of metallurgical microscope, the magnetic signals were scanned by TSC-1M-4. The magnetic memory signals of quenched and tempered steel specimen are significantly lower than that of the non-quenched and tempered steel specimen. After eliminating stress by quenching the specimen, the results show that different stress states have significant effect on the magnetic field characteristics of the specimen.