The invention belongs to the medicine technical field, and more particularly relates to a dipeptidase inhibitor compound, the pharmaceutically acceptable salt and the isomer thereof shown in the formula (I); wherein, the R<1>, Ar, X, m and n are defined in the specification. The invention also relates to preparing methods of the compounds, 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.