Abstract Vibrational loading was introduced as an innovative method to improve the thermoplastic formability of Zr35Ti30Be26.75Cu8.25 bulk metallic glass in a supercooled liquid state. The tensile strain, as a measure to characterize the formability, increased with increasing loading frequency, indicating a vibrational loading facilitated formability. The physical mechanism of this phenomenon was rationalized on the basis of both theoretical analysis and finite-element-method simulation. The theoretical analysis revealed that a more homogeneous distribution of flowing units with a smaller volume, together with a larger free volume concentration, existed in the specimen under relatively higher loading frequencies. The finite-element-method simulation combined with the free volume constitutive relation exhibited an increase in free volume concentration with increasing loading frequency, in agreement with theoretical analysis. Finally, compressive and hot-embossing tests under vibrational loading were carried out to further verify the applicability of this technique. The present results not only provide an effective method to facilitate the thermoplastic formability of bulk metallic glasses, especially in micro/nanoscale forming, but also offer a better understanding of the structural evolution of the metallic supercooled liquid under vibrational loading.