The invention discloses a preparation method of an edible packaging film based on diatom polysaccharide. The preparation method specifically comprises the following steps: degreasing diatom powder, concretely adding a chloroform methanol mixed solution into the diatom powder, carrying out degreasing, suction filtration, and drying to obtain degreased diatom powder; preparing the diatom polysaccharide, concretely uniformly mixing the degreased diatom powder with water, then adding 8-chlorotheophylline, and carrying out ultrahigh-pressure extraction and suction filtration, wherein the obtained filtrate is the water extracted crude polysaccharide; and preparing the edible packaging film, concretely taking the following components in parts by weight: the diatom polysaccharide, glycerol, gelatin, tea polyphenol and water, dissolving the components to prepare a film liquid, carrying out degassing, then uniformly pouring the degassed film liquid into a mold, and carrying out drying for forming a film, so as to obtain the edible packaging film. The preparation method disclosed by the invention has the beneficial effects that the preparation method is simple and feasible, the time consumption is low, the energy consumption is low, the utilization rate of the raw materials can be improved, and the degradable pollution-free packaging film with good performance can be formed. The surface of the packaging film is smooth and compact, the film is easy to uncover, and the packaging film is edible, is easy for industrial scale production and has good application value and market potential.