The invention discloses a food preservative film and a preparation method thereof. The preparation method comprises the following steps: heating and mixing modified sodium alginate, ascorbic acid, stearic acid, acetic acid, an emulsifier and water for the first time to obtain a film forming solution A; adding chitosan and polylysine to the film forming solution A, and performing heating and mixingfor the second time to obtain a film forming solution B; mixing low density polyethylene resin, the film forming solution B, polyethylene glycol monopalmitate, polyvinyl alcohol, aluminum phosphate and synthetic vegetable ester, and performing blow molding to obtain the food preservative film. The problem that the traditional preservative film still has many defects in light transmittance, tensile strength, water vapor transmission coefficient, water solubility, swelling degree and the like is solved.