Abstract: To discuss the effects of the flange gap on the cumulative fatigue damage,three types of tower flange gap are established.Several non-linear factors including the contact existed in flange-flange and flange-washer,as well as the pretension for bolts are taken into account. The relationship between the external tension and internal force for bolts can thus be achieved. Furthermore,the influence of the opening height and the length of the gap on the internal force for bolts are investigated. The resultant fatigue damage using Schmidt-Neuper method reveals that the special shape of the gap possesses significant impact on the fatigue damage. The proposed method can provide the theoretical reference for the design and manufacturing of the tower flange.