The invention discloses preparation methods of an antioxidant, a water-retaining agent, a mixture and a modified fuel cell membrane electrode. The invention discloses a preparation method of the modified fuel cell membrane electrode, which comprises the following steps: a) preparing an antioxidant, or a water-retaining agent, or a mixture with antioxidant and water-retaining functions, and preserving the mixed solution for later use; b) coating two sides of a microporous reinforced membrane with the mixed solution obtained in the step a) by using a coating device, and drying the membrane to obtain a modified perfluorosulfonic acid proton exchange membrane; c) processing the modified PEM membrane to prepare the fuel cell membrane electrode. The invention further discloses a formula and a preparation method of the antioxidant, a formula and a preparation method of the water-retaining agent, a formula and a preparation method of the mixture with antioxidant and water-retaining functions, and applications of all the products hereinabove in the fields of membrane electrodes and fuel cells. According to the invention, the chemical structure degradation phenomenon of the proton exchange membrane caused by free radicals is effectively relieved, the lasting water retention performance of the proton exchange membrane is improved, the proton conductivity is improved, and the mechanical property of the membrane electrode is improved by adopting the enhanced microporous membrane, so that the stability of the membrane electrode is enhanced, and the service life of the membrane electrode is prolonged.