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.%在外应力作用下铁磁晶体应力能会增加，其相应的总自由能也会增加，而改变铁磁晶体的磁化状态会消耗能量，并趋向于自由能最低．通过对45号调质钢和非调质钢试件分组进行三点弯曲疲劳裂纹扩展试验和金相显微镜在位显微观测，并利用TSC-1M-4检测磁场信号，发现调质钢试件的磁记忆信号明显低于非调质钢试件的磁记忆信号，在对试件调质消除内应力后，不同的应力状态对试件的磁场特征信号具有显著的影响．
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