Abstract: WC-10Co4Cr coatings were fabricated by high-velocity oxygen-fuel spraying technology (HVOF) with the nano-structure, submicron-structure and regular microstructure. The influence of grain size on the decarburization of WC powder particles during the deposition processes was studied, and the effects of WC grain size on the microstructure, microhardness distribution, fracture toughness, and interfacial bonding strength were investigated systematically. In the results, with the increasing of the WC grain size, the WC decarburization and porosity of the WC-10Co4Cr coatings firstly increase and then decrease, while the microhardness and fracture toughness firstly decrease and then increase, and the interfacial bonding strength shows a trend of gradual decrease. The Weibull analysis of microhardness for the submicron-structured and regular microstructured coatings exhibits a bimodal distribution under the indentation load of 100 g, whereas the coatings with three kinds of microstructures exhibit a monomodal distribution under the indentation load of 300 g, which is mainly attributed to the mutual effect of the WC decarburization, interlaminar binding force, and porosity of the coatings. The nanostructured coating exhibits the best comprehensive performance of low decarburization, high interfacial bonding strength, superior microhardness, and fracture toughness.