In the present work，normal carbon source black carbon was substituted by graphene which was dispersed in N-Methyl-2-pyrrolidone and was used to prepare nanocrystalline WC-Co composite powders using short process in-situ reduction and carbonization reaction method. The results show that graphene as carbon source could reduce reaction temperature, and the particles diameter of WC-Co composite powders distribute slightly. Composite powders were consolidated through spark plasma sintering system and the mean grain size of WC in WC-Co cemented carbides is about 290nm. Vickers hardness and fracture toughness of the bulk was 1387.7?3.1kg/mm2 and 8.3?.1MPa?m1/2. The interfaces between WC/WC, WC/Co and WC/C were studied through HRTEM images and had grain boundaries with low misfit.