The invention relates to a functional protective film. The functional protective film is prepared through the following steps that a, 7.7% of ethylenediaminetetraacetic acid, 2.5% of citric acid, 5.5% of fluoboric acid, 4.6% of monoethanolamine, 3% of fluosilicic acid and 76.7% of water are weighed by weight to prepare a mother solution; b, a protective film solution is blended and a protective film is generated, wherein the mother solution is added with water on the basis of the proportion of 5-10%, and the protective film solution is formed; then, to-be-treated metal charge with no oil or rust is placed into the protective film solution, treatment is performed under normal temperature for 5-7 min, and the functional protective film is formed on the surface of the metal charge. The functional protective film contains no heavy metal, no harm is caused to the human body, and the functional protective film is used under normal temperature, and is short in treatment time, good in corrosion resistance and good in adhesive force.