Starch is the polymerization of glucose molecules, which is the most common storage form of carbohydrates in cells. Starch, also known as starch in the catering industry, has the general formula of (C6H 10O5)n, and when it is hydrolyzed to disaccharide, it is maltose with the chemical formula of C12H2O1.After complete hydrolysis, monosaccharide (glucose) is obtained with the chemical formula of C6h/kloc-0. Starch includes amylose and amylopectin. The former is a spiral structure without branches; The latter is composed of 24~30 glucose residues connected end to end by α- 1,4- glycosidic bond, and α- 1,6- glycosidic bond at the branch. Amylose is blue when it meets iodine, and amylopectin is purple when it meets iodine. This is not a chemical reaction between starch and iodine, resulting in interaction, but that the central hole of the starch helix can just hold iodine molecules, and through van der Waals force, they form a blue-black complex. Experiments show that the single iodine molecule can't make the starch blue. In fact, it is the iodine molecule ion (I3) that makes the starch blue.