The invention relates to a preparation method of tetramisole hydrochloride, and aims at solving the problems that the conventional preparation method of tetramisole hydrochloride is complex in process and the yield is low. The preparation method comprises the following steps of: firstly, heating and reacting styrene oxide and ethanol amine so as to obtain an addition product; secondly, adding an organic solvent and lewis acid into the addition product, controlling the reaction temperature and adding thionyl chloride so as to obtain a chlorination product; thirdly, adding deionized water into the chlorination product, dropping NaOH solution, subsequently dropping concentrated HCl and thiourea, heating and refluxing, cooling and separating a cyclization product; fourthly, mixing the cyclization product with concentrated HCl and lewis acid, adding NaOH solution so as to adjust the pH of the system, and heating and reacting so as to obtain a tetramisole product; and fifthly, adding deionized water into the tetramisole product, dropping concentrated HCl, and subsequently increasing the temperature and reacting so as to obtain tetramisole hydrochloride. According to the preparation method, tetramisole hydrochloride is synthesized by using a five-step method, the process is simple, the yield of each step can be more than 85%, and the yield is high.