Abstract: In accordance with the coexistence theory of metallic melts structure involving compound formation and Fe-Al phase diagram as well, and by means of regression analysis, the structral units of Fe-Al melt at 1 315℃ and 1 600℃ have been determined. On the basis of these structural units, the calculating models of mass action concentrations have been deduced. The agreement between calculated values of N_Fe, N_Al and measured α_Fe,α_Al respectively is satisfactory.