Thread damage of the bolts used in the skirt board structures of a high-speed train is analyzed in this study. An experimental study on the loosening behaviour and fatigue fracture of bolted structures is conducted. After the tests, the thread damage and the fracture morphology of bolts are studied. The experimental results show that fatigue wear is the main wear mechanism of the used bolts. The increase in the amplitude of cyclic transverse displacement worsens the thread damage and increases the loosening degree of bolted structures. The bolts fracture in fatigue, and the fatigue life obeys normal distribution when the amplitude of cyclic transverse displacement is large. The fracture morphology of bolts exhibits ductile fracture with dimples.