A preparation method of a high-barrier antibacterial flame-retardant food packaging film solves problems that an existing food packaging film is non-degradable, poor in preservation effect, and inflammable. The preparation method includes: performing blending reaction on chitosan quaternary ammonium salt and phytic acid to generate a polyelectrolyte complex; and adding the polyelectrolyte complex into a polyvinyl alcohol solution, heating the polyvinyl alcohol solution added with the polyelectrolyte complex to obtain a film-forming solution, pouring the film-forming solution into a mold, leveling and drying the film-forming solution to obtain the high-barrier antibacterial flame-retardant food packaging film. The food packaging film has water vapor permeability in 1.82-2.58×10−8 g·s−1·m−1·Pa−1, oxygen permeability in 1.63-12.31 cm3·mm−2·Pa−1·day−1, and a value of limiting oxygen index (LOI) in 28.10%-33.33%. The food packaging film performs an instant self-extinguishing behavior after ignition; and can inhibit Staphylococcus aureus and Escherichia coli when used in packaging.