NOVELTY - An ionic liquid is added to a container and a sulfonated polyether ether ketone film is immersed in the ionic liquid. Then, the composite film is removed and the liquid adsorbed on the surface of the composite film is wiped out. The composite film is immersed in deionized water, and a phosphoric acid solution is added to the container, and the composite film is immersed into the phosphoric acid solution for 1-48 hours, and the container is sealed, to obtain a phosphoric acid-doped sulfonated polymer composite film with self-assembling structure.    USE - Phosphoric acid-doped sulfonated polymer composite film.    ADVANTAGE - The phosphoric acid-doped sulfonated polymer composite film has excellent stability, mechanical performance and conductive performance.    DETAILED DESCRIPTION - An ionic liquid is added to a container and a sulfonated polyether ether ketone film having sulfonation degree of 40-80% is immersed in the ionic liquid. The container is closed and placed in an oven and reacted for 0.5-2 hours. Then, the temperature of the reaction system is reduced to room temperature, and the composite film is removed and the liquid adsorbed on the surface of the composite film is wiped out. The composite film is immersed in deionized water at room temperature, water is changed for every 10-30 minutes and immersed for 1-3 hours. The composite film is removed and the liquid adsorbed on the surface of the composite film is wiped out. The water content in the composite film is evaporated and the composite film is clamped between two Teflon (RTM: fluoropolymer) plates and placed in oven until the weight is constant and naturally cooled to room temperature. A phosphoric acid solution is added to the container, and the composite film is immersed into the phosphoric acid solution for 1-48 hours, and the container is sealed, to obtain a phosphoric acid-doped sulfonated polymer composite film with self-assembling structure. The ionic liquid comprises chloro-1-butyl-3-trimethylimidazole or 1-butyl-3-trimethylimidazole hexafluorophosphate.