L-thiazolidine-4-formic acid ethyl ester hydrochloride is an important heterocyclic compound including N and S, widespreadly used in the fields of green pesticides, immune-medicine and new materials because of its special chemical structure. Through two reaction steps of condensation and esterification, L-thiazolidine-4-formic acid ethyl ester hydrochloride was synthetized with L-cysteine hydrochloride as the raw materials. By the method of single factor experiment, the synthesis process of L - margaret-4-formic acid ethyl ester hydrochloride was optimized, the products were characterized by melting point, IR spectrum and mass spectrum. The results show that the optimum synthetise conditions of condensation reaction are that the molar ratio of L-cysteine hydrochloride to formaldehyde, the reaction temperature and the reaction time are 1∶1.2, 400 ℃ and 4 h respectively. The optimum synthetise conditions of esterification reaction are that the reaction temperature and the reaction time are 700 ℃ and 4 h respectively. The characterization results of the two step reaction products show that the products are respectively the target products. The equipments of the synthesis process are simple, and easy to operate. The process conforms to the industrialized mass production needs.