Theoretical investigation of the phase equilibira of three kinds of Fe-based alloys, Fe-Ni, Fe-Pd and Fe-Pt systems is attempted by combining FLAPW total energy calculations and Cluster Variation Method. It is revealed that the magnetism plays a crucial role in the phase stability and spin polarized calculation is indispensable. The experimental L10-disorder transition temperatures are reproduced with fairly high accuracy. Thermal vibration effects incorporated based on the Debye-Gruneisen model further improve the calculated transition temperatures. Furthermore, the influence of the various effective cluster interactions on phase stability is calculated systematically.