The invention discloses a preparation method of thiomorpholine-1,1-dioxide hydrochloride and a preparation method of thiomorpholine-1,1-dioxide. The preparation method of thiomorpholine-1,1-dioxide hydrochloride includes the following steps that firstly, a thiomorpholine amino protection compound and potassium permanganate which is added into a reaction system in batches are subjected to an oxidation reaction to generate a thiomorpholine-1,1-dioxide amino protection compound; secondly, the thiomorpholine-1,1-dioxide amino protection compound obtained in the first step is hydrolyzed under the hydrochloric acid condition, and thiomorpholine-1,1-dioxide hydrochloride is obtained. When the thiomorpholine amino protection compound and potassium permanganate are subjected to the oxidation reaction in the preparation method, a batch-wise addition mode is used, the oxidation effect is good, and the reaction is sufficient. Meanwhile, the situation that a lot of heat is dissipated in a short time in the oxidation reaction can be avoided, the reaction process is smooth and easy to control, and operation is safer.