Multiple characterization techniques including DSC, TEM, XRD, HV and SEM were utilized to investigate the structural evolution of metallic glass (MG) under elastic cyclic loading. It is found that the relaxation enthalpy (served as the reflection of free volume contents) in the fatigued specimen was raised by ∼5 times as compared with as-cast specimen. The cyclic loading induces the larger interatomic distance and smaller coordination number. Besides, the microhardness reduction from ∼545.6 ± 15.3 to ∼518.7 ± 4.8 was observed in the as-cast and fatigued specimens, indicating the cyclic loading induced softening behavior. Such results reveal that the elastic cyclic loading can cause the irreversible structural change with the increase of free volume. Then the key problem of shear band formation under cyclic stress level lower than yield strength was clarified by the free volume theory.