Cluster-plus-glue atom model and cluster-line criterion were employed to optimize the compositions of Zr-based Al–Ni–Zr alloys with superior glass-forming abilities (GFAs). Alloy series along the four composition lines, namely Ni 3 Zr 7 –Al x , Ni 3 Zr 8 –Al x , Ni 3 Zr 9 –Al x and Ni 4 Zr 9 –Al x (x = 1, 1.5, 2, 3) were designed and their GFA and thermal stabilities were investigated systematically in this work. It was revealed that the best glass former was Al 2 Ni 4 Zr 9 (i.e., Al 13.3 Ni 26.7 Zr 60 in atomic percent) alloy, where almost fully amorphous rod with a diameter of 10 mm could be obtained by copper mold suction casting. The GFA indicators, T g /T l (0.579) and γ m (0.689), of the Al 2 Ni 4 Zr 9 bulk metallic glass are all larger than those of the reported optimum Al 15 Ni 25 Zr 60 glass former. Two cluster formulas [Ni–Ni 2 Zr 9 ](Al 2 Ni 1 ) or [Ni–Al 2 Zr 9 ]Ni 3 were tentatively proposed to explain the present optimal glass-forming composition Al 2 Ni 4 Zr 9 , where clusters Ni 3 Zr 9 and Al 3 Zr 9 (the central Al being replaced with Ni in the proposed formula) are derived from the Al 2 NiZr 6 crystalline phase.