NOVELTY - An electrolyte preparing method involves preparing a preliminary purify acidic alkaline extract by performing reduction and extraction process to prepare high pure quadrivalent vanadyl sulfate solution comprising quinquevalent vanadium acid sodium solution, followed by adding impurity-removing agent to silicate and chromium radical solution to form precipitate, which is filtered to remove impurity. The pH of the resultant precipitate is adjusted, followed by removing aluminum salt, magnesium salt and calcium salt with vanadium silicate solution, chromate, and phosphate anionic impurities.    USE - Method for preparing electrolyte for use in all-vanadium redox flow battery.    ADVANTAGE - The method enables preparing electrolyte with high purity in a simple and inexpensive manner.    DETAILED DESCRIPTION - An electrolyte preparing method involves preparing a preliminary purify acidic alkaline extract by performing reduction and extraction process to prepare high pure quadrivalent vanadyl sulfate solution comprising quinquevalent vanadium acid sodium solution, followed by adding impurity-removing agent to silicate and chromium radical solution to form precipitate. The resultant precipitate is filtered to remove impurity. The pH of the resultant precipitate is adjusted to 8-11, preferably 9, followed by removing aluminum salt, magnesium salt and calcium salt with vanadium silicate solution, chromate, and phosphate anionic impurities to obtain mixture. The pH of the mixture is adjusted to 10-11, followed by removing carbonate, vanadium sulfide solution, metal impurity cations, aluminum salt and silicate substance at a mole ratio of 1:1-1:1.2, calcium and phosphate at a mole ratio of 1:0.7-1:1.2, carrying out alkaline extraction on raw liquid with alkaline extraction agent, using weak alkaline ammonium chloride solution for extraction, purifying pentavalent vanadium solution, using 30-40% quaternary ammonium salt as extraction agent, and kerosene as diluent for extraction to obtain extracted solution. The pH of the extracted solution is adjusted to 5-9 using ammonia or weakly acidic solution of ammonium chloride, followed by extracting solid phase ratio at 1: 5 and 1:1, adding reducing agent in vanadate precipitate, adjusting acidity, reducing vanadate to vanadyl sulfate by using hydrazine hydroxylamine as inorganic, and organic material, oxalic acid as a reducing agent, sulfuric acid as inorganic acid, acetic acid adjusting solution as organic acid, adjusting pH to less than 1, reducing ammonium metavanadate vanadyl sulfate, extracting vanadyl sulfate by using acidic extracting agent to obtain extract, carrying out sulfuric acid extraction, purifying vanadyl sulfate solution, using neutral oxygen-containing compound and acid phosphorus-containing compound and 30-40% phosphate ester as extracting agent, 5-10% phosphate as synergist, sulfonated kerosene as diluent for extraction process, and using 3-4 M sulfuric acid as stripping agent, controlling extraction phase ratio at 1:1, controlling stripping phase ratio at 1:1. The extracting agent is stripped with sulfuric acid raffinate with ammonia water, sodium hydroxide, calcium carbonate or barium carbonate to obtain stripped product. The pH of stripped product is adjusted to 2-3. The extraction is carried out for 4-6 times to complete extraction process to obtain vanadyl sulfate solution. The vanadyl sulfate solution is degreased by using activated carbon to remove residual organic phase to obtain high pure vanadyl sulfate solution. The activated carbon is washed by acid washing and water, followed by carrying heat treatment to remove organic and inorganic impurities. The activated carbon is added with impurity stripping solution, heated, cooled and filtered to obtain a finished product.