Objective This work aims at solving the problems that the ultrafine/nano WC-Co raw powders were easy to suffer from decarburization during thermal spraying and thus preparing the ultrafine/nanostructured cermet coatings with excellent comprehensive properties such as high hardness, toughness, wear resistance and surface quality for extending their applications in industries. Methods The ultrafine and nanoscale WC-Co composite powders were prepared in batch by the in-situ synthesis technique. Through a granulation process, the composite powders were agglomerated into the thermal spray feedstock powders, which had good spherical shape and high density while keeping the original ultrafine/nanostructures. After that, the ul-trafine-structured WC-based coating with low decarburization and high density was obtained using the high velocity oxy-fuel spraying. Results The content of W2C in the coating could be greatly decreased by reducing the porosity of the feedstock particles. By optimizing the spray parameters, the prepared ultrafine-structured coating had hardness above 1450 HV0.3, and toughness increased by over 40% as compared with the conventional micron-scaled coatings. Thus, the ultrafine-structured coating had better wear resistance at different testing conditions. Conclusion The cemented carbide coatings prepared by using the ultrafine or nanoscale WC-Co composite powders with the in-situ synthesis technique have excellent comprehensive properties. The composite powders are applicable to prepare coatings that meet demands of high hardness, wear resistance, toughness and surface quality as high-quality spraying materials.