A polymer ion exchange membrane for acidic electrolyte flow battery. The membrane is nitrogen heterocycles aromatic polymer, especially polybenzimidazole type polymer. A nitrogen heterocycles in the membrane interact with acid in the electrolyte to form donor-receptor proton transport network, so as to keep the proton transport performance of the membrane. The preparation condition for the membrane is mild, and the process is simplicity. The preparation method is suitable for mass production. The membrane is used in acidic electrolyte flow battery, especially in vanadium flow energy storage battery. The membrane has excellent mechanical stability and thermostability. In vanadium redox flow battery, the membrane has excellent proton conduct performance and excellent resistance to the permeation of vanadium ions.