Magnetic stability of a Fe-Cr-Co permanent magnet material at high temperatures has been investigated. Changes of microstructures and hyperfine field distributions after high temperature holding were analyzed by transimission electron microscopy (TEM) and Mossbauer spectroscopy. The results of experiments indicate that the changes of magnetic properties of the Fe-Cr-Co alloy tend to decrease, and then gradually keeps a certain level with increasing the holding time at high temperature. TEM observations show that microstructures of the alloy do not change distinctly after high temperature holding. Hyperfine interaction study through Mossbauer spectroscopy finds that the composition difference between alpha(1), and alpha(2) phases increases, and the composition of the two phases fluctuates. This study attributes the change of magnetic properties to element redistribution of Cr atom rather than the change of microstructure.