Preparation method of tiamulin alkali

The invention relates to a preparation method of tiamulin alkali. The preparation method comprises the following steps of: adding pleuromutilin in a chlorinating agent in a solvent for chlorinating, and then adding thiourea for reacting to obtain a solution; chlorinating 2-diethylaminoethanol in the solvent by using the chlorinating agent to obtain a chloride solution of 2-diethylaminoethanol; and mixing two solutions together to react, controlling the reaction temperature and reaction time, dewatering and drying the obtained product, and evaporating the solvent so as to obtain tiamulin alkali. The yield of tiamulin alkali can be more than 80%. The reaction method for preparing tiamulin alkali is simple and easy to control; and 2-diethylaminoethanethiol which has fetid smell and is limited application is abolished, so that the preparation method has a good commercial prospect.