The invention provides a novel preparation method of L-alanine isopropyl ester hydrochloride, and relates to a preparation method of an intermediate of a new drug sofosbuvir for treating chronic hepatitis. The method sequentially comprises the following steps that L-alanine is adopted as a raw material to react with triphosgene for ring closure, after ring opening is conducted through isopropanol under the acidic condition, salt formation is conducted, and the product L-alanine isopropyl ester hydrochloride is obtained. According to the novel preparation method, a brand-new synthetic route is provided, the adopted raw material is wide and sufficient in source, the cost is low, the reaction conditions are mild, the processes are simple, all the reactions are conventionally operated, the condition that a large quantity of high-irritation raw materials such as thionyl chloride are used is avoided, and a good industrial prospect is achieved.