A snapshot mechanism of a data processing system is provided herein. The snapshot mechanism includes providing a snapshot storage unit for storing the data created when snapshotting the target storage units and generating a plurality of snapshot images accordingly. Two different types of address tables in the snapshot image are used for corresponding to the storage units of the snapshot storage unit and the target storage units. The status of the target storage units can be recovered to the status at a predetermined time ago according to the snapshot images. The two types of address tables are respectively used for storing the data created by the data processing system and history data so as to prevent the data stored in the target storage units to be overwritten.