Abstract: Based on the self-designed testing equipment for bolted joints, the self-loosening behaviour of the TiCN/MoS₂ coated bolts, which were connected with the TiCN/MoS₂ coated nuts and the uncoated nuts respectively, was systematically studied under transverse alternating load. After tests, the morphologies of the damaged threads were analyzed using three-dimensional microscope, scanning electron microscope, energy dispersive X-ray and white light interferometer. Furthermore, the wear mechanisms were investigated on the first thread surfaces. The results showed that the thread damage of the TiCN/MoS₂ coated bolts was slighter than that of the uncoated bolts, and the self-loosening degree of the TiCN/MoS₂ coated bolts was lower than that of the uncoated bolts under the same experimental parameters. Moreover, under the same equivalent stress as that of the uncoated bolts at the thread root, the preload of the TiCN/MoS₂ coated bolt can be improved by about 10%, the damage of the thread surface was further reduced, and the self-loosening degree of bolted joints was also decreased. In addition, delamination was the main wear mechanism on the first thread surface of the composite coated bolts.