Abstract: A α'-phase structure is got after Fe-69.7%(atom)Cr alloy aging for four years at 500℃. Its M?ssbauer spectrum characteristic is determined. The results indicate the M?ssbauer spectrum obtained at 300 K is a pure Lorentzian lineshape, the overall width of composite absorbed spectrum increases considerable with temperature droping, and the range of superfine field reaches about 3 072.20kA/m at 77 K. The behaviour of superfine field is similar to that of ideal paramagnetic model. This phenomenon demonstrates that the α'-phase is a paramagnet above 77K. By thermal cycling treatment from 1200℃ to room temperature, a considerable acceleration of Cr atom diffusion to grain boundaries and α'-phase precipitation in Fe-24.6%Cr-5%Al alloy occurres, and which cause the alloy embrittlement.