Supersonic plasma spraying has been used to deposit WC-12Co coatings on polished stainless steel and aluminum substrate surface. The microstructure was observed by SEM and the bond mechanism was analyzed. It can be seen that individual WC particles can embed the substrate and make the substrate surface rough. The substrate materials differ, the depth that WC embed is also different. Bond among coatings mainly belonged to mechanical bonding. Bond between coatings and substrate mainly belonged to mechanical bonding, and partially belonged to metallurgy bonding, physical bonding, diffusion and micro-forging.