Abstract: The relation of contact fatigue failure mode and acoustic emission (AE) amplitude for plasma spraying coating is investigated under different stress levels, and contact fatigue failure mechanism is analysed. The results show that contact fatigue failure mode has no obvious relation with contact stress according to AE amplitude during fatigue failure phase. Spalling or delamination failure tends to happen at the AE amplitude of 87 to 93 dB. Pitting failure tends to happen at the AE amplitude of 78 to 83 dB. Pitting failure is mainly caused by adhesion wear generated in rolling contact between rough salient on coating surface and bearing balls, and by three body abrasion among coating, abrasive particles and bearing balls. Spalling failure is associated with cracks initiation and growth in coating surface microdefects and surface wear behavior. Internal delamination is controlled by maximum shear stress in the coating. Interface delamination is associated with interface shear stress, lower bond strength and thermal mismatch between coating and substrate.