Disclosed are a protective starch-based film and its preparation method and application, belonging to the field of food packaging. According to the method for preparing the protective starch-based film, surfaces of zinc oxide nanoparticles are enabled to adsorb tannic acid and iron ions under the action of metal coordination by controlling the pH to obtain metallic polyphenol network coated zinc oxide nanoparticles, dispersion of the obtained nanoparticles is added to a starch gelatinization solution, and a melanin-like precursor is simultaneously added to form mixed liquid; and by controlling the pH of the mixed solution, π-π stacking, self-polymerization and metal coordination are induced, so that a stable protective starch-based film with a nano-reinforced interpenetrating network structure is formed. The method is simple, green, pollution-free and energy-saving, and the prepared starch-based degradable film has remarkable ultraviolet-shielding, mechanical and antibacterial properties, thus having wide application prospects in the field of food packaging.