A preparation method of nano 
tungsten carbide comprises the following steps: (1) dissolving 
ammonium metatungstate, 
chromium nitrate and a water-soluble 
carbon source substance into in heated deionized water, sufficiently mixing, and performing 
spray drying, wherein the weight percentage of the water-soluble 
carbon source substance is 10-30%, the weight percentage of the 
chromium nitrate is 0.5-2% and the temperature of the deionized water is 70 DEG C; (2) performing auxiliary 
hydrogen reduction on powdery carbon obtained in the step (1), and before discharging the 
powder out of a furnace, passivating the 
powder with an 
inert gas, wherein the temperature is 710-850 DEG C, the heating rate is 10-15 DEG C /  min and the reaction time is 2-5h; (3) annealing 
tungsten powder obtained in the step (2) at high temperature, wherein the annealing temperature is 1000-1300 DEG C and the annealing time is 1-3h; and (4) carbonizing the 
tungsten powder obtained in the step (3), and before discharging the powder out of the furnace, passivating the powder with the 
inert gas, wherein the carbonizing ratio is 6.21wt.%, 
hydrogen is used as a protective 
atmosphere, the carbonizing temperature is 1100-1400 DEG C and the carbonizing time is 1-4h. The particle size of the prepared 
tungsten carbide is 60-90nm; after the prepared 
tungsten carbide is crushed, agglomeration-free nano 
tungsten carbide powder can be obtained; the environment is polluted; and the development of a nanocrystalline WC-Co hard 
alloy can be effectively promoted.