the present invention provides a pharmaceutical composition for the treatment of 2 type diabetes , wherein the pharmaceutical composition contains - 7 -- butyryl ]- 3 - trifluoromethyl - 5 , 6 , 7 , 8 - tetrahydro - imidazopyrazine - 1 - carboxylic acid methyl ester or its pharmaceutically acceptable salts and metformin or its pharmaceutically acceptable salts , preparation method thereof and method of treating 2 type diabetes with the composition .