Abstract: This paper quantitatively analyzes the influence factors of the magnetic properties of the ferromagnetic material under the external magnetic field from a microscopic point of view, and calculates the three-axis weakening of the ferromagnetic material under the external magnetic field of different directions and strengths. The detection characteristics of the magnetic signal are studied and the system experiments are carried out. The research results show that: the spontaneous magnetization vector of the magnetic domain tends to rearrange in the direction of the stress to produce a weak magnetic signal; the weak magnetic signal has a peak in the axial direction and a peak-to-peak value in the radial direction, and at the zero crossing point, it fluctuates irregularly in the circumferential direction. The intensity of the magnetic field increases and the weak magnetic signal also increases, but the magnitude of the increment gradually decreases, and the influence of the external magnetic field on the weak magnetic signal tends to be saturated; the external magnetic field has a weak influence on the weak magnetic signal in the vertical direction.