Abstract: Irradiation can induce genomic instability and produce a series of delayed mutations. As a free-error repair mechanism of post-duplication, mismatch repair plays an essential role in the maintenance of genomic stability. Mismatch is proposed a kind of conservative repair mechanism. Not only can it be involved in the repair process directly by heter-dimers, but it can affect the cell-cycle by cdc2 phophatized path to supervise the cell-cycle indirectly. Therefore, discussing the relation of genomic instability and mismatch repair may represent one of aspects of radiational damage and repair mechanisms