Abstract:  Let X_n be the totally ordered set  of n element  and O_n be  the order preserving transformation semigroup of  X_n, a new class   subsemigroups  O_n,r of  semigroup  O_n was introduced.  The structure characteristic of  the largest regular subsemigroup of semigroup  O_n,rwas characterized. Moreover, the generated rank  of  semigroup O_n,r  was characterized by analyzing the largest regular subsemigroup. The obtained results developed the corresponding conclusions of other relevant literatures.