Abstract: In order to study the critical stress and metal magnetic memory signal characteristics of ferromagnetic materials before and after the yield point, based on the density functional theory, a magnetic coupling model was established based on the theory of solid energy band, and the crystal of ferromagnetic crystal under stress was calculated. The change of lattice structure, differential charge density, etc., and the steel pipe compression test were designed under different pressures. The results show that as the stress increases, the atomic bonding force in the crystal gradually decreases, which affects the lattice stability. When a certain degree of stress concentration is reached, the atomic magnetic moment suddenly changes to cause phase transformation inside the crystal and the abrupt changes of magnetic memory signal. The difference of magnetic memory signals before and after yielding is analyzed from the experimental point of view, and the feasibility of using the first principle method to study the magnetic mechanics relationship of ferromagnetic materials is proved.