Abstract: A three dimensional finite element model for a new type anti-loosening nut and a standard nut were established in the commercial package ABAQUS, and both fitted with standard bolts. The changing trend of the preload and microslip of an engaged screw between a standard bolt and nut after lock under a transverse cyclic load were analyzed. Then with the same initial preload, the residual preload and microslip of the engaged screw of a new type anti-loosening nut under certain transverse loads were compared with a standard nut. It is found that under transverse cyclic loads, the decrease of the preload and microslip of the engaged screw were responsible for the loosening of bolt connections. Also, an initial preload has comparatively large influence upon the percentage of a residual preload and microslip of an engaged screw, and the preload should be increased as high as possible. Meanwhile, this anti-loosening nut has good ability of resisting self-loosening, which is correlated to the test result. Finally, the variations of additional bending moment with different preloads was investigated, when the anti-loosening nut work.