NOVELTY - A vanadium ion flow battery electrolyte comprises vanadium salt, sulfuric acid, deionized water, an additive for improving electrolyte solubility and stability, and metal salt soluble to the sulfuric acid line.    USE - A vanadium ion flow battery electrolyte.    ADVANTAGE - The vanadium ion flow battery electrolyte can greatly improve hydrogen overpotential of negative and positive electrode systems of a vanadium battery. The ratio of gas separation in the electrolyte caused by various polarization in an operation process of the vanadium battery is greatly reduced. The stability of the electrolyte in a charging/discharging process is improved. The preparation method of the vanadium ion flow battery electrolyte saves the step of making tervalent vanadium and tetravalent vanadium electrolyzed by obtaining the sulfuric acid-vanadium oxide solution containing 50% vanadium electrolyte, thus greatly simplifying the production process of directly charging and discharging, reducing the loss of the vanadium in the preparation process and reducing the production cost of the electrolyte.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method of preparing the vanadium ion flow battery electrolyte, comprising uniformly mixing vanadium trioxide and vanadium pentoxide to gradually add dense sulfuric acid solution, and heating and stirring until a solid is completely solved to form a vanadium-containing solution; adding alkali hydroxide to the vanadium-containing solution and adjusting to a certain pH value, and filtering; and adding the additive and the metal salt into the filtered solution to obtain the vanadium ion flow battery electrolyte; and    (2) a vanadium ion flow battery, comprising two electrolyte pools respectively holding the negative and positive vanadium ion flow battery electrolytes; and layers of battery units overlapped together.    Each battery unit comprises a graphite felt, a graphite plate, a flow frame, a membrane, and a gasket. The membrane divides a single battery into a positive semi-battery and a negative semi-battery. Each electrolyte pool is provided with a pump and connected with liquid inlet and outlet of negative and positive electrodes of the battery set through a sealing pipeline.