The invention provides a method for preparing hydroxyethyl starch 200/0.5. According to the method, sticky rice starch is taken as a raw material, ethylene oxide is taken as an etherifying agent and isopropanol is taken as a reaction solvent. The production process of the method comprises steps such as mixing, gelatinization, hydrolysis, etherification, neutralization, refining, drying and the like. By adopting the method, dextran hydroxyethyl starch 200/0.5 of which the molecular weight and the substitution degree both meet the requirements can be prepared, and moreover the method is simple in preparation process, small in side reaction and high in product yield.