This invention relates to a method to prepare pramipexole hydrochloride, which includes the contact reaction between (S)-(-) 2-amino-6-propylamido-4, 5, 6, 7-tetrahydrobenzothiazole and hydrogen chloride. To prepare (S)-(-) 2-amino-6-propylamido-4, 5, 6, 7-tetrahydrobenzothiazole, (-) 2-amino-6-propionamido-4, 5, 6, 7-tetrahydrobenzothiazole reacts with NaBH4 and BF3 in tetrahydrofuran under the protection of inert gas and then (S)-(-) 2-amino-6-propylamido-4, 5, 6, 7-tetrahydrobenzothiazole is separated from the mixture. The preparation method of (S)-(-)2-amino-6-propylamido-4, 5, 6, 7-tetrahydrobenzothiazole dihydrochloride from the hydroboration reduction and salt formation of (-)2-amino-6-propionamido-4, 5, 6, 7-tetrahydrobenzothiazole as raw materials provided in this invention has the advantages of simple and easily obtainable raw materials and soft reaction conditions, and operation is thus easy to control and the reaction security is promoted.