The basic properties of corn starch and a new method of corn starch preparation are introduced. After corn is soaked, it is coarsely crushed. After separating embryos, crude starch milk is obtained. The crude starch milk is finely crushed, and proteins and fibers are separated. A starch milk is obtained, and an alkali solution is added to the starch milk to form a starch solution. The temperature of the starch solution is 40℃. to 60℃., the starch solution is filtered to obtain amylose and amylopectin, and the amylose is dissolved. In alkaline solution, while amylopectin is not easily soluble, amylose and amylopectin are separated by filtration. The amylose and amylopectin are directly separated during the process of preparing corn starch by the process of separating the amylose and amylopectin through the different solubility of amylose and amylopectin in hot water, 18.91% of the upper layer was centrifuged for the first time. The product was mainly long amylose.