An operating method for a data storage device is provided. The operating method includes steps of: dividing a mapping table into a plurality of sub-mapping tables; receiving an access command comprising a data address and a command category; determining whether a target sub-mapping table corresponding to the data address has been cached, wherein the target sub-mapping table is one of the sub-mapping tables; and if false, reading and caching the target sub-mapping table from the sub-mapping tables.