Disclosed a preparation method of a green, biodegradable, and multifunctional collagen-based nanocomposite film, and overcomes the problems of difficult biodegradation, poor barrier property, and single function of food packaging materials in the existing technologies. The present invention includes the following steps: adding silicate nanosheet into deionized water for ultrasonic dispersion; then adding polyphenolic acid into the mixture, wherein a mass ratio of the polyphenolic acid to the silicate nanosheet is 1:(0.2˜1); and adjusting the pH value to 3.0˜4.0 to obtain a solution A; adding collagen with a concentration of 5 g/L into an acetic acid solution, and fully dissolving the collagen to obtain a solution B; isovolumetrically mixing the solution A with the solution B, stirring at room temperature, and adjusting the pH value to 4.5˜5.5 to obtain a casting solution; and pouring the casting solution into a polytetrafluoroethylene mold, and naturally drying to obtain a nanocomposite film.