System and method for producing 3.5-valence high-purity vanadium electrolyte

A system and method for producing a 3.5-valence high-purity vanadium electrolyte, comprising hydrolyzing high-purity vanadium oxytrichloride into vanadium pentoxide in a fluidized bed, and reducing vanadium pentoxide into a low-valence vanadium oxide having an average vanadium valence of 3.5 adding water and a sulfuric acid solution under a microwave field applied externally for dissolution at a low temperature, to obtain a 3.5-valence high-purity vanadium electrolyte. The preparation of vanadium pentoxide by means of gas-phase hydrolysis in the fluidized bed is of short process and high efficiency. By providing an internal member within the reduction fluidized bed, the precise regulation of the valence state of the reduction product is achieved, and the special chemical effect of the microwave field is used to promote dissolution of the vanadium oxide and activate the vanadium ions, thereby greatly improving the activity of the electrolyte.