The delaminateion wear mechanism of the arc sprayed coatings was studied by analyzing coatings structural feature and stress distribution on the worn surface. The coating surface was subjected to alternately tensile stress and compression stress caused by normal load and friction force during sliding. In a certain depth below the surface, there exists maximum shear stress. Therefore fatigue damage will take place at subsurface of the coating under alternate stress. The adhesion strength between splats of coating is by far lower than casting material because of lamellar structure. And the adhesion strength between splats is further weakened due to the defects, such as porosity and micro-crack, appearing mostly on the boundaries between thin oxide sheets and splats. When the fatigue damage accumulates to a certain value, micro-cracks initiate at the defects between splats. Then these micro-cracks grow, connect, and propagate along the defects between splats. Finally, these cracks shear to the coating surface leading to spallation of the splats, and thus wear debris is generated. By repeating the above process, delamination of the coatings will occur.