Aimed at the problem of metal magnetic memory that the microcosmic cracks cannot be evaluated quantitatively by the metal magnetic memory testing method at present, the numerical value relation between the magnetic conductivity and stress is derived based on the analysis of the metal magnetic memory testing mechanism by using the theory of Jiles, who discussed the physical mechanism of the stress-magnetization effect. The finite element analysis of stress-magnetization effect is done on steel plate specimen with a microcosmic crack using ANSYS. Through the analysis, using an applicable magneto-elastic coupling model and distilling the peak value's distance and peak value of metal magnetic memory can evaluate the breadth and deepness of microcosmic cracks quantitatively.