The invention provides a preparation method of thioether and belongs to the technical field of pharmacy. The preparation method comprises the steps of making 3-bromopyridine-4-mercaptan and alkali reagent react for 5-40 hours in organic solvent at a first reaction temperature, and obtaining reaction mixed liquor; then getting the obtained reaction mixed liquor to make contact with methyl 2-bromoisobutyrate, and conducting a reaction for 0.5-30 hours at a second reaction temperature; obtaining a thioether compound through after-treatment. The preparation method is simple in operation, capable of effectively reducing generation of impurities and obtaining a high-purity product and suitable for industrialized production.