Abstract: Eight kinds of nanostructured WC-12Co coatings were prepared by high velocity oxygen fuel (HVOF) spraying technology on Q235 steel substrate with different barrel lengths and spray distances.Phases of the feedstock powders and coatings were analyzed by XRD.The surface morphology of spraying powders and sprayed coatings was analyzed by SEM.The microhardness of the coatings was also tested.The results indicate that the barrel length is the key factor to control the decomposition of nanostructured WC during spraying.The coatings deposited by using long barrel experienced more severe decarburization but showed higher microhardness than those coatings deposited by using short barrel.When the barrels length was the same,spray distance also had some effect on the phases,surface morphology and microhardness of the coatings.