Three different WC grain size powder were used to prepare WC-Co coatings employing HVOF technique. The effect of WC grain size on the abrasive wear resistance and failure mechanism were analyzed. The results show that the abrasive wear resistance increases with the decrease of WC grain size. Nanostructured coating is high in surface plasticity. It can only be pressed out of prints, the opportunity of cutting is small. Micro-cutting wear dominates the main abrasive wear mechanism of nanostructured coating.