The invention belongs to the medicine technology field, particularly relates to a new dipeptidase-IV inhibitor compound, the pharmaceutically acceptable salt and the isomer thereof; wherein, the R<1>, R<2>, Ar, n, X or Y are defined in the specification. The invention also relates to preparing methods of the compounds and the drug combination containing the compounds and the applications of the compounds in preparing the medicine for treating or preventing diabetes, non-insulin-dependent diabetes, hyperglycemia and insulin resistance.