The pharmaceutically acceptable salts of methyl (R)-7-[3-amino-4-(2,4,5-trifluoro-phenyl)-butyryl]-3-trifluoromethyl-5,6,7,8-tetrahydro-imidazo [1,5-a]pyrazine-1-carboxylate, their preparation methods and their use for preparing anti-diabetic medicaments are disclosed.