The formation, oxidation, and agglomeration of wear debris of coatings were investigated in this study. The rheology of the third body and its influence on the fretting wear behavior were studied in depth and systemically. The results showed that the shape and nature of the debris were the essential factors determining the mobility of the third body. All factors that could make the debris layer or third body remain on the contact surfaces would decrease the friction coefficient and fretting wear. The soft and large plate-like debris particles were apt to remain in the contact region. Conversely, the hard and sphere-shaped debris particles tended to be squeezed from the contact surfaces and to increase the fretting wear.