NOVELTY - Dried polyetheretherketone is sulfonated, added to ice-water bath, filtered, washed, dried, and dissolved in solvent to obtain a solution. Dried perfluorosulfonated resin is dissolved in solvent and heated to obtain a solution. Both solutions are mixed, heated, and ultrasonically processed. A polypropylene membrane is soaked in half the solution and dried to obtain a composite membrane. The remaining solution is added on the composite membrane, dried, and demolded to obtain a perfluorosulfonated resin/sulfonated polyetheretherketone composite membrane.    USE - Preparation of perfluorosulfonated resin/sulfonated polyetheretherketone composite membrane for separators of vanadium redox flow batteries.    ADVANTAGE - The method enables simple and economical preparation of perfluorosulfonated resin/sulfonated polyetheretherketone composite membranes having excellent stability and vanadium resistance.    DETAILED DESCRIPTION - Dried polyetheretherketone (1 part weight) is added to 95-98% concentrated sulfuric acid (10-70 parts weight) and sulfonation is carried out. The product is added to an ice-water bath, stirred, pressure-reduced, filtered, washed till neutral, and dried to obtain sulfonated polyetheretherketone. The sulfonated polyetheretherketone is dissolved in a high-boiling-point organic solvent to obtain a solution with a volume ratio of 1/5-1/100 g/ml. Dried perfluorosulfonated resin is dissolved in a high-boiling-point organic solvent and heated in a reaction kettle to obtain a solution with a mass fraction of 2-40%. Both solutions are mixed in a volume ratio of 1/2-3/1, stirred for 2-8 hours, heated for 1-4 hours at 40-140 degrees C, and ultrasonically processed to remove air bubbles and impurities. Half of the mixed solution is added to a glass plate with a groove and a polypropylene membrane is soaked in the solution at 30-120 degrees C for 1-12 hours. The membrane is dried to obtain a composite membrane. The remaining solution is added on the surface of composite membrane, dried, and demolded in deionized water to obtain a perfluorosulfonated resin/sulfonated polyetheretherketone composite membrane.