Abstract: Thread connection is a common structural form of aeronautic equipment. Damage and failure often occur to this kind of structure, but wear failure is an uncommon failure form of joint thread. Through macroscopic and microscopic observation, metallographic inspection, hardness testing and dimension measurement, the wear mechanism and cause of joint thread were analyzed. The results show that the wear mode of the thread is fretting wear, which was caused by the increase of contact pressure and displacement amplitude due to the relatively small pre-tightening force and the small working height of the thread.