Glass-forming ability/range of the Cu–Zr–Ni ternary system was studied by thermodynamic calculations and ion beam mixing of multilayered films. Thermodynamic calculations located an energetically favored composition region for metallic glass formation, and also characterized the composition dependence of the glass-forming ability. Under the guidance of the thermodynamics calculations, four sets of nano-sized Cu–Zr–Ni multilayered samples were designed, prepared and then subjected to irradiation by 200 keV xenon ions. It turned out that unique amorphous phases were indeed obtained in the samples Cu21Zr55Ni24 and Cu24Zr45Ni31 that were located in the predicted superior glass-forming ability region, while for the Cu33Zr17Ni50 and Cu68Zr19Ni13 samples that fell within the low glass-forming ability region, ion beam mixing resulted in the formation of amorphous-crystalline dual-phase structures. A brief discussion was also presented for the formation mechanisms of the amorphous phase and the amorphous-crystalline composites.