The invention provides a method for refining metformin hydrochloride in the technical field of chemical synthesis. The invention adopts a technical proposal that: a crude product of metformin hydrochloride obtained through synthesis of dimethylammonium chloride and dicyandiamide is put into a purified water of which the weight is three times of that of the crude product of metformin hydrochloride, heated to 65 to 75 DEG C for circumfluence, and added with a concentrated hydrochloric acid of which the weight is 2 percent of the weight of the unqualified metformin hydrochloride for treatment, is cooled and crystallized to separate a mother liquid; and thus a refined metformin hydrochloride is obtained. The obtained metformin hydrochloride is qualified in clarity with a qualification rateof 100 percent, and satisfies requirement.