The invention discloses a preparation method of a polypeptide raw material aspartic acid beta-tert-butyl ester alpha-methyl ester hydrochloride, and mainly solves the technical problems of complex original process, long period, low yield, high cost, high dangerousness and inadaptation for mass production. The preparation method comprises the following steps: firstly, suspending aspartic acid in dry tetrahydrofuran, to prepare aspartic lactonic anhydride hydrochloride under the action of phosphorus oxychloride; secondly, suspending aspartic lactonic anhydride hydrochloride in methanol, carryingout a reaction to obtain aspartic acid alpha-methyl ester hydrochloride, and adjusting the pH value by triethylamine to make aspartic acid alpha-methyl ester separated out; thirdly, suspending aspartic acid alpha-methyl ester in dichloromethane, introducing isobutylene, dropwise adding concentrated sulfuric acid, and carrying out sealed reaction treatment, to obtain an oily substance aspartic acid beta-tert-butyl ester alpha-methyl ester; and fourthly, dissolving the oily substance aspartic acid beta-tert-butyl ester alpha-methyl ester in ethyl ether and dropwise adding ethyl ether-hydrochloric acid gas, to obtain the final product aspartic acid beta-tert-butyl ester alpha-methyl ester hydrochloride.