The Fe-Gd and Co-Fe-Gd systems were optimized by means of the CALPHAD （CALculation of PHAse Diagram） technique. The solution phases, liquid, bcc, fcc and hcp, were described by the substitutional solution model. For the Fe-Gd system, the compounds Fe23Gd6,Fe3Gd and Fe2Gd with no solubility ranges were treated as stoichiometric compounds. According to the CaCu5-type structure of the intermetallic compounds Fe17Gd2,it was reasonable to adopt a three-sulattice model （Fe2,Gd）Gd2Fe15 in the Fe-Gd system, and this model was also adopted as （Co2,Fe2,Gd）（Co2,Gd）2（Co,Fe）15 to describe the compounds （Co,Fe）17Gd2 and （Co,Fe）5Gd in the Co-Fe-Gd ternary system. The other compounds were treated as the line compounds （Co,Fe）mGdn and no ternary compound had been reported in the Co-Fe-Gd system. The thermodynamic description of the Co-Fe and Co-Gd system were taken from literatures. A self-consistent thermodynamic description of the Co-Fe-Gd system was obtained.
