Glass-forming ability of multicomponent Gd (Tb)-Co-Al alloys was predicted by multicomponent Miedema model theory and equivalent bond parameter theory. The pre-designed alloy samples were prepared by casting the melt ingots into a water-cooled copper mould with various diameters such as 1, 3, 5 mm. The structure of the alloy samples were analyzed by X-ray diffraction. The glass transition, crystallization and melting behavior of the alloys were investigated by differential scanning calorimetry (DSC). The result shows that the multicomponent Miedema model theory and the equivalent bond parameter theory are effective on composition design of bulk amorphous alloys, and the experimental outcome approximately accords with the theoretical prediction.