High-purity metformin hydrochloride preparation method

The invention discloses a high-purity metformin hydrochloride preparation method. N-methyl pyrrolidone is used as a solvent, dicyandiamide and dimethylamine hydrochloride are taken as a solute, the solvent and the solute are added into a synthesis kettle for reaction, and metformin hydrochloride is prepared through steps of stirring, cooling, spin-drying, washing, crystallizing and drying. The metformin hydrochloride prepared through the preparation method provided by the invention has the advantages that the yield is higher than 96.4 percent, and the product purity is higher than 99.93 percent.