NOVELTY - An organic diacid of polybenzimidazole intermediate (I) comprises side chain containing fluorine.    USE - An organic diacid of polybenzimidazole intermediate used in preparing polybenzimidazole films, polybenzimidazole/phosphoric acid composite proton exchange film materials, separation films, sensors, high temperature resisting fiber and composite materials, and binders (claimed).    DETAILED DESCRIPTION - Organic diacid of polybenzimidazole intermediate of formula (I) comprises side chain containing fluorine.R=F p- or m-substituted Ph, or CF3 p- or m- substituted Ph.    An INDEPENDENT CLAIM is included for:    (1) a method of preparing organic diacid compound by carrying out refluxing reaction to fluorine-containing halogenated compound of formula (R-X), 3,5-dimethyl phenol, catalyst and methylbenzene in organic solvent for 2-8 (preferably 6 hours) at 120-170 degrees C, discharging methylbenzene, heating to 120-170 degrees C, reacting to obtain m-dimethyl benzene derivative of formula (II), and oxidizing in solvent with oxidant for 2-48 (preferably 10)hours;    (2) a polybenzimidazole polymer of formula (III) having number-average molar mass of 10000-200000; and    (3) a method of preparing polybenzimidazole polymer by mixing organic diacid compound, composite diacid monomer, tetramine monomer and polyphosphoric acid under the protection of inert gas, and reacting at 60-80 degrees C to 160-250 degrees C.    The composite diacid monomer is m-phthalic acid, terephthalic acid, 2,6-dicarboxyl pyridine, 3,5-dicarboxyl pyridine, 1,4-di(4-carboxyl)-phenoxy-benzene, 1,3-di(4-carboxyl)-phenoxy-benzene, 1,3-di(3-carboxyl)-phenoxy-benzene, 1,4-di(3-carboxyl)-phenoxy-benzene, 1,2-ditrifluoromethyl-3,4-di((4-carboxyl)-phenyl) methane or 5-sodium thiosulfate-m-phthalic acid. The tetramine monomer is 3,3',4,4'-tetramino diphenyl ether, 3,3',4,4'-tetramino diphenyl, 1,2,4,5-tetramino benzene, 3,3',4,4'-tetramino diphenyl sulfone, 3,3',4,4'-tetramino diphenyl ketone or 1,2-dimethyl-3,4-di(4-(3,4-diamino phenoxy)-benzene)yl-methane    n, m=0-1000; and    X=Cl, Br or I.