Aiming at the problem that the bolt connection structure was prone to loosening under transverse vibration，the axial force attenuation curves of bolts under different displacement amplitudes were obtained by transverse vibration test，and the influence of displacement amplitude on the loosening behavior of 30CrMnSiA bolt connection structure was studied.The attenuation curve of the bolt axial force was obtained through transverse vibration tests.The damage morphologies of the contact thread surfaces were characterized using optical microscopy，scanning electron microscopy，and white light interferometry，while the chemical composition of the damaged areas was analyzed via energy dispersive X-ray spectroscopy.The results indicate that the degree of bolt loosening increases significantly with the displacement amplitude.Specifically，the loosening degree rises from 2.7%（at A_f=0.10 mm） to 13.8%（at A_f=0.35 mm），accompanied by aggravated damage on the contact thread surfaces.When the displacement amplitude exceeds 0.25 mm，a secondary rapid decline stage emerges in the axial force during the loosening process.Moreover，the dominant wear mechanism of the thread surfaces transitions from being primarily abrasive wear and adhesive wear under small displacement amplitudes to being predominantly fatigue wear under large displacement amplitudes.Consequently，the loosening behavior of the bolted joint is governed by the interfacial wear mechanism，which is critically regulated by the displacement amplitude.