Magnetic stability is an important indicator of permanent magnet materials. The stability of magnets is directly related to the reliability of permanent magnets. As an important functional material, magnetic materials have been widely used in key devices such as aerospace and high-performance space vehicles. For magnetic parts used in a space environment, good stability is required, including stability under temperature, shock vibration, strong electromagnetic fields, and particle radiation conditions. Improving the stability of magnetic materials is an important task of high reliability, high precision, and high stability required by magnetic devices used in aerospace systems and high-performance weapon systems. Among the various factors that affect the stability of permanent magnetic materials, temperature has the most significant effect on the stability of the material. Permanent magnets are generally used as magnetic field sources to provide a constant magnetic field within a certain air gap. Most of the magnets work in the open circuit state. The magnetic induction intensity of the permanent magnet in the working state is not at the Br point in the closed circuit state, but at a certain point on the demagnetization curve lower than Br, that is, the operating point of the permanent magnet. The working point of the permanent magnet is related to the shape of the demagnetization curve and the size of the demagnetizing field HD of the magnet. Therefore, the size of the demagnetizing field of the magnet in the working state in the design of the magnetic device needs to be considered. NdFeB rare earth permanent magnets are very sensitive to temperature, and at the same time, the influence of temperature on magnetic properties has a certain size effect. Magnets with different demagnetization fields have different resistance to external magnetic field interference, and the thermal demagnetization behavior of magnets is also different. These characteristics cannot be ignored in the design of magnetic devices.