The invention provides a method for preparing an all-vanadium redox flow battery electrolyte by a combination of resin exchange and chemical deposition. According to the method, a solution containing soluble vanadate is used as the raw material; and the all-vanadium redox flow battery electrolyte is prepared by the methods of ion exchange resin adsorption, analysis and deposition. According to the method, the solution containing soluble vanadate is used as the raw material; and the high-purity and high-concentration vanadium electrolyte which is required by the all-vanadium redox flow battery is prepared by the combination of the methods of resin exchange and chemical deposition. The method has simple steps and low requirement on the equipment; the raw material and the reagent used in the preparation process are relatively low in cost; impurities can be removed conveniently; and the industrial preparation of the high-purity and high-concentration vanadium electrolyte can be realized easily.