The preparation method comprises the steps that vanadium slag, a calcium-based additive and return slag are roasted at first, a vanadium-containing spinel structure in the vanadium slag is damaged and decomposed under the action of the calcium-based additive and the return slag during. . The preparation method comprises the steps that vanadium slag, a calcium-based additive and return slag are roasted at first, a vanadium-containing spinel structure in the vanadium slag is damaged and decomposed under the action of the calcium-based additive and the return slag during. . Ammonium metavanadate can be converted into vanadium oxides with different valence states through different heat-treatment processes. Ammonium metavanadate or vanadium pentoxide are often used in industry as raw materials to prepare vanadium trioxide. The common inorganic reducing agents for the. . The invention relates to the field of industry, in particular to a preparation method of high-purity ammonium metavanadate for an all-vanadium redox flow battery. The component and composition of the prepared electrolyte by AMV were analyzed by X-ray diffraction (XRD) and inductively coupled plasma (ICP).