In order to study the loosening mechanism of the flange joint bolt in the lateral vibration,the transverse fretting wear test of simulated fasteners was carried out by means of transverse vibration fatigue testing machine,and then the pretightening force and pre-loading of bolt joints under different lateral loads and frequencies were observed.,and measure the amount of wear and surface damage. The experimental results show that the bolt preload reduction is divided into two stages:the plastic deformation stage in which the pre-tightening force decreases rapidly and the fretting wear stage in which the pre-tightening force decreases slowly. The pre-tightening torque drop is divided into three stages:the first stage is not obvious due to the high local contact stress;the second stage is rapidly degraded due to the plastic deformation,and the third stage bolt enters the fretting wear. At the third stage,the pre-tightening torque begins to slowly decrease. Under low frequency vibration of the bolt,the amount of mass change is not sensitive to small changes in frequency. The surface wear of the bolt in contact with the clamp increases as the alternating amplitude load increases;it decreases as the frequency increases.