The invention discloses a method for synthesis of 1-(4, 5-dihydro-2-thiazolinyl)-3-mercaptoazetidine hydrochloride. With 2-methylthio-2-thiazoline (I) as the raw material, the method of the invention comprises the steps of: in the presence of alkali, reacting 2-methylthio-2-thiazoline (I) with 3-hydroxyazetidine hydrochloride so as to obtain 1-(4, 5-dihydro-2-thiazolinyl)-3-hydroxyazetidine (II), and reacting (II) with methyl sulfonylchloride in the presence of alkali so as to obtain 1-(4, 5-dihydro-2-thiazolinyl)-3-methane sulfonate group azetidine (III), subjecting (III) to a reaction with potassium thioacetate so as to obtain 1-(4, 5-dihydro-2-thiazolinyl)-3-thioacetic acid ester group azetidine (IV), in the presence of alkali, subjecting (IV) to hydrolysis and then to acidification with dilute hydrochloric acid, thus obtaining the 1-(4, 5-dihydro-2-thiazolinyl)-3-mercaptoazetidine hydrochloride (V). With easily available and inexpensive starting material, the method of the invention simplifies the synthesis route, improves the raw material utilization ratio and the overall yield. An intermediate obtained in the reaction can be subjected to refinement by a recrystallization method or to a next reaction directly, so that the yield is high and the "three wastes" produced during the reaction process are few. In addition, with low cost, the method of the invention is beneficial for industrial production.