NOVELTY - Preparing proton conducting membrane containing branched sulfonated polyimide comprises: (i) preparing triethylamine salt type branched sulfonated polyimide film by adding 2,2'-benzidinedisulfonic acid, triethylamine, and m-cresol into reactor, stirring, adding 1,3,5-tris(4-aminophenoxy)benzene and 4,4'-diaminodiphenyl ether, stirring, dissolving 1,4,5,8-naphthaleneteracarboxylic dianhydride and benzoic acid in m-cresol, placing in constant pressure dropping funnel, heating, pouring on glass plate and drying; and (ii) placing the prepared film in an organic solvent, soaking and washing.    USE - The proton conducting membrane is useful for preparing vanadium redox battery and fuel cell.    ADVANTAGE - The proton conducting membrane has good performance.    DETAILED DESCRIPTION - Preparing proton conducting membrane containing branched sulfonated polyimide comprises (i) preparing triethylamine salt type branched sulfonated polyimide film under nitrogen atmosphere by adding 1.6-6.4 mM 2,2'-benzidinedisulfonic acid, 4.8-19.2 mM triethylamine, and 1/2-4/5 m-cresol (to the total volume of 60-185 ml) into the reactor, stirring at room temperature dissolve, adding 0.32-4 mM 1,3,5-tris(4-aminophenoxy)benzene and 0-1.6 mM 4,4'-diaminodiphenyl ether, stirring to dissolve, dissolving 8 mM 1,4,5,8-naphthaleneteracarboxylic dianhydride and 9.6-16 mM benzoic acid in remaining amount of m-cresol, placing in constant pressure dropping funnel in order to add in drop-wise manner into the reactor, heating to 40-100 degrees C for 15-24 hours, pouring the reaction material onto a glass plate for casting the film, where the thickness of the film 10-200 mu m and drying at 60-150 degrees C for 10-30 hours and (ii) placing the triethylamine salt type branched sulfonated polyimide film in an organic solvent for 10-30 hours, soaking in 1.0-2.5 mol/l sulfuric acid aqueous solution for 10-36 hours, washing with demineralised water for 2-4 times to neutralize and storing in deionized water.