(1) Pretreatment of raw materials: firstly, impurities such as meat quality and dirt of shrimp shells and crab shells are removed, washed and dried; (2) Acid leaching: removing inorganic salts from raw materials. Soak the pretreated shrimp and crab shells in 5% dilute hydrochloric acid for 2 hours at room temperature, then filter and wash them with water to neutrality; ③ Digestion: protein and fat in raw materials are removed. Boiling the shrimp and crab shells soaked in acid in 10% sodium hydroxide solution for 2h, then filtering, washing with water to neutrality, and drying to obtain chitin; (4) Decolorization: There are three methods, including sun bleaching, bleaching with oxygen in the air under the action of sunlight and ultraviolet rays under the condition of keeping slight acid moist; Chlorination and decoloration with potassium permanganate and sodium bisulfite; You can also use organic solvents such as acetone to extract color. 5 Deacetylation: deacetylation of chitin. Chitin was hydrolyzed in 45%-50% sodium hydroxide solution at 100- 1 10℃ for 4 hours, then filtered, washed with water to neutrality, and dried to obtain chitosan.