Abstract: The method of metal magnetic memory is a new potential nondestructive testing method, which can be used to detect and estimate the residual stress and micro-damages of the ferromagnetic items. The samples of steel 45 are studied on the self-designed tension loading equipment. The effectiveness of the method is proved by the comparative analysis of the magnetic intensity, the gradient of the magnetic intensity and the value of X-rays diffraction on the samples surface. The mechanism that the method detects the residual stress and micro-damages is preliminary explained on the point of the magnetic physics.