In this example, vanadium oxytrichloride (with a purity of above 5N) was used as a raw material, and the throughput was 3000 kg/h. In the liquid phase hydrolysis reaction tank 2-1, clean water (having a resistivity of 18.0 MΩ·cm) and vanadium oxytrichloride were added in a mass ratio of 3, and the operation temperature was set to be 50° C., to obtain a slurry of vanadium pentoxide. The slurry entered the washing filter 2-2 to be subjected to washing with clean water (having a resistivity of 18.0 MΩ·cm) and filtration, to obtain washing liquid and vanadium pentoxide precipitate powder, wherein the washing liquid was transmitted to the wastewater treatment system, and the vanadium pentoxide precipitate was preheated by the preheating system and then entered the reduction fluidized bed. In the reduction fluidized bed 5, the reducing gas introduced was hydrogen gas, the volume fraction of hydrogen gas in the mixed gas of the hydrogen gas and coal gas introduced into the reduction fluidized bed 5 was 50%, the average residence time of the powder was 30 min, and the operation temperature was 550° C., and a low-valence vanadium oxide having an average vanadium valence of 3.5 and a purity of 99.997% was obtained. In the dissolution reactor, electronic-grade concentrated sulfuric acid and clean water (having a resistivity of 18.0 MΩ·cm) are added, and the dissolving temperature was 50° C. In the activation device 11, activation was conducted for 150 minutes with an ultraviolet power density of 100 W/m³, and an activation temperature of 30° C., to obtain a high-purity vanadium electrolyte with a total impurity content of less than 5 ppm (except for the effective components).