Abstract: Based on the loosening failure behavior of bolt connections under transverse vibration, a displacement loading transverse vibration test system was designed. By exploring single-bolted joint structures, loosening failure tests of bolt connection under different working conditions were conducted. This study investigated the change in preload during loosening process and the wear on the thread tooth surface before and after failure. A finite element model of the bolt connection structure consistent with the test piece was established. Based on the simulation results, the pair surface slippage and bearing surface stress distribution of thread under transverse vibration were analyzed, and the reasons for the bolt connection’s loosening failure were revealed. The results indicate that the bolt loosening process can be roughly divided into three stages: linear loosening, rapid loosening, and complete loosening. When the vibration amplitude was reduced from 0.8 mm to 0.5 mm, the loosening rate decreased by approximately 71%. When the initial preload was increased from 8 kN to 12 kN or from 12 kN to 16 kN, the loosening rate decreased by about 34%. When the thread pitch was minimized from 1.5 mm to 1.25 mm, the loosening rate reduced by about 41%. Under the transverse vibration, alternating bending load can be produced in the thread tooth, which causes serious wear on the edges and corners of the tip thread, as well as uneven wear across the thread surface. Furthermore, slippage occurs on the thread surface due to the transverse vibration, which disrupts the self-locking state between the bolt and the nut, and producing loose torque. Under transverse vibration, the bearing surface between bolt head and lower plate was more unstable compared to the bearing surface between the nut and upper plate. Consequently, the bolt tends to loosen more readily than the nut.