NOVELTY - 3-10 Wt.% sulfonic acid resin solution is sprayed in back-side surface of the polytetrafluoroethylene microporous membrane, leveled using three-pressure rollers, and dried in an electric oven at 120-240 degrees C for 1-35 minutes, to obtain crosslinked polytetrafluoroethylene microporous membrane. 10-25 Wt.% sulfonic acid resin solution is sprayed in side surface of the crosslinked polytetrafluoroethylene microporous membrane, leveled using three-pressure rollers, and dried in an electric oven at 120-240 degrees C for 1-35 minutes, to obtain reinforced polytetrafluoroethylene microporous film.    USE - Preparation of reinforced polytetrafluoroethylene microporous film used as proton-exchange membrane.    ADVANTAGE - The method provides reinforced polytetrafluoroethylene microporous film having high electroconductivity and excellent mechanical strength, by an economical process.    DETAILED DESCRIPTION - Air is electrostatically blown to microporous structure of expanded polytetrafluoroethylene microporous membrane surface in blowing air volume of 10-330 CFM for 0.3-100 seconds, electrostatic treatment is performed by soaking the membrane in analytically-pure ethanol at 15-35 degrees C for 0.5-24 hours, and solvent evaporation process is carried out at 15-45 degrees C for 0.1-6 hours. 3-10 Wt.% sulfonic acid resin solution is sprayed in back-side surface of the polytetrafluoroethylene microporous membrane, leveled using three-pressure rollers at 80-100 degrees C, 110-200 degrees C and 180-250 degrees C for 10-100 minutes in roller speed of 0.01-0.8 m/minute, and dried in an electric oven at 120-240 degrees C for 1-35 minutes, to obtain crosslinked polytetrafluoroethylene microporous membrane. 10-25 Wt.% sulfonic acid resin solution is sprayed in side surface of the crosslinked polytetrafluoroethylene microporous membrane, leveled using three-pressure rollers at 80-100 degrees C, 110-200 degrees C and 180-250 degrees C for 10-1000 minutes in roller speed of 0.01-0.8 m/minute, and dried in an electric oven at 120-240 degrees C for 1-35 minutes, to obtain reinforced polytetrafluoroethylene microporous film. The starting temperature of the electric oven is 35-65 degrees C. Sulfonic acid resin is dissolved in 10-25 wt.% mixture containing methanol, ethanol and propanol or 3-10 wt.% mixture of N,N-dimethylformamide and N,N-dimethylacetamide, at 100-300 degrees C for 3-24 hours, to obtain sulfonic acid resin solution. The volume ratio of methanol, ethanol and propanol is 4-9:4-10:5-7. The concentration of mixture of N,N-dimethylformamide and N,N-dimethylacetamide is 3-10%. The volume ratio of N,N-dimethylformamide and N,N-dimethylacetamide is 5-15:7-9. The methanol, ethanol, propanol, N-dimethylformamide and N,N-dimethylacetamide are analytically pure. The polytetrafluoroethylene microporous film has thickness of 1-3 mu m, pore size of 0.2-2 mu m and porosity of 80-90%.