The invention discloses a preparation method of vanadium diboride powder, belonging to the technical field of ceramic powder preparation. The preparation method is characterized by uniformly mixing ammonium metavanadate, boron powder and a certain amount of molten salt and then carrying out heat treatment on the mixture at 800-1100 DEG C for 0.5-4 hours under the protection of an inert gas, thus obtaining the vanadium diboride powder, wherein the mole ratio of ammonium metavanadate to boron powder is 3:11; the byproducts generated after reaction, namely diboron trioxide and molten salt, can be removed by soaking the byproducts in hot water to dissolve the byproducts. The preparation method has the technical effects that the vanadium source adopted in the method is non-toxic and harmless; the preparation method is simple in production process and is suitable for volume production; the molten salt environment introduced in the method increases the diffusion velocity of solid phase matters, so that the synthesis temperature is low and the synthesis cycle is short; and the synthesized powder has the characteristics of high purity, small grain size and the like.