The work aims to prepare a coating agent based on seaweed extract, characterize its physical and chemical properties, and use it for the preservation of mango coating preservation, to study its preservation effect. Edible Sargassum sargassum was subject to ultrasonic extraction with hot water, and water-soluble chitosan was added to prepare a seaweed coating agent. The seaweed coating agent was transformed into a seaweed film by solvent evaporation method, and its physical and chemical properties, including surface morphology, hydrophilicity, tensile strength and gas barrier property, were characterized. Mango was soaked with seaweed coating agents with different dilution times (10, 20, 50), and stored at room temperature (23±1) ℃ for 12 days. The fruit appearance, color, weight loss rate, hardness, soluble solid, titrable acid and other indicators were determined at day 0, 3, 6, 9, 12. The structure of the seaweed film was compact and uniform, with high mechanical strength, good hydrophilicity, high water permeability and low oxygen permeability. The seaweed coating agent (dilution ratio 10) could effectively reduce the weight loss rate of fruit, maintain fruit hardness, reduce fruit decay rate, inhibit fruit respiration, reduce the consumption of soluble solids and titrable acids, and improve the activity of antioxidant enzymes. The seaweed coating agent with edible Sargassum extract as the main component and water-soluble chitosan as the auxiliary film forming agent has good film forming property and mango preservation effect, which provides a useful reference for the wide application of seaweed extract in the field of fruit preservation.