The magnetic components in power supplies are naturally sensitive to external magnetic fields, and their operating characteristics directly affect the output characteristics of the power supply. Modeling the background magnetic field is an important prerequisite for the study of the interference of magnetic components in power supplies by strong stray magnetic fields, but few studies have focused on this application scenario, and the commonly used methods for electromagnetic field analysis are difficult to balance accuracy and efficiency. In this paper, we propose a method to analyze the influence of stray magnetic fields based on the equivalent magnetic circuit network method, which discrete the research object into magnetic circuit units, equivalently form a network model, and obtain the field distribution of the model by solving the equations of the equivalent magnetic circuit system. We take a toroidal ferrite core as an example, and use the equivalent circuit network method to calculate the field distribution of the toroidal core under DC excitation and uniform orthogonal magnetic field, and analyze the effect of the background magnetic field on its equivalent inductance. By comparing the results of the equivalent circuit network method with those of the finite element method, the accuracy and efficiency of the proposed analysis method are demonstrated, and it is shown that the method is applicable to the analysis of power supplies disturbed by the background magnetic field.