Unique amorphous alloys are synthesized at the compositions of 25 and 40 atom % of W by ion beam mixing in the equilibrium immiscible Sc-W system characterized by a positive heat of formation of +14 kJ/mol. In thermodynamic modeling, a Gibbs free energy diagram is constructed based on Miedema's theory, and the diagram predicts a glass-forming range of the Sc-W system to be within 12-58 atom % of W. To develop an atomistic model, ab initio calculations are first conducted to assist the construction of an n-body Sc-W potential under the embedded atom method. The proven realistic potential is applied in molecular dynamic simulations to study the crystal-to-amorphous transition in the Sc-W solid solutions, thus determining the glass-forming ability of the system to be within 15-50 atom % of W. Apparently, both theoretical predicted glass-forming ranges cover the experimentally measured one, showing an excellent agreement. We report, in this paper, the experimental results from ion beam mixing and the multiscale theoretical modeling concerning the amorphous alloy formation in the Sc-W system together with a brief discussion of the structural transition mechanism.