The mechanism of the direct electrochemical reduction of solid oxides Tb2O3-Dy2O3-Fe2O3 was studied by cyclic voltammetry and chronoamperometry measurements. The reduction process was then proved by the constant potential electrolysis for different time. Five cathodic current peaks in the cyclic voltammogram were observed, supporting a mechanism of five-step processes for the electrochemical reduction of Tb2O3-Dy2O3-Fe2O3. The first peak represented the electrochemical reduction reaction of Fe2O3→Fe, while other peaks could be confirmed as the electrochemical reduction reactions between Fe and Tb2O3 as well as Dy2O3. The following electrochemical reduction sequence was confirmed by XRD analysis. Firstly Fe2O3 was electrolyzed to form Fe, then intermetallic Tb-Fe and Dy-Fe were electrolyzed from Fe and Tb2O3 as well as Dy2O3, and finally they were alloyed to form TbDyFe2. The above electrochemical reduction results could be explained by a theory of “diffusion at triplephase boundary lines”, and hereby the triplephase boundary lines were Fe|Fe2O3|CaCl2 and Tb-Dy-Fe|Tb2O3-Dy2O3|CaCl2 in the electro-reduction process