Nano-sized vanadium and chromium carbides composite powders were prepared by mechanical alloying assisted microwave heating method using micron size vanadium oxide, chromium oxide and carbon black nanoparticles as raw materials. The products were characterized by XRD, XPS, TG-DSC, SEM, TEM and BET techniques. The results showed that the optimum synthesis conditions of nano vanadium /chromium carbides composite powders were obtained as follows: mass fraction of carbon black 35%, reaction temperature 900℃, and holding time 1 h. Under these conditions, the reaction products are mainly composed of V3Cr2C5, Cr2VC2 and Cr3C2. The particles are spherical or nearly spherical with good disper-sion and no obvious agglomeration. The average particle size is about 50 nm and the specific surface area is 115.53 m2/g. The addition of nano vanadium and chromium carbides composite powders can enhance the mechanical properties and grinding efficiency of vitrified bond cBN grinding tool, which reduces the wastage of the grinding tool, and has a good friction-reducing effect.