The present invention relates to a salt form of (R)-methyl-2-(3-aminopiperidin-1-yl)-3-(2-cyanobenzyl)-4-carbonyl-3,4-dihydrothiophene[3,2-d]pyrimidine-6-carboxylic acid and a preparation method for the salt form. Also disclosed is a pharmaceutical composition of the formula I compound salt form. The salt form of the present invention provides powerful in vivo hypoglycemic activity and is expected to be a novel pharmaceutical active ingredient for treating or preventing diabetes mellitus type 2 and/or complications of diabetes mellitus type 2.