A hard disk system state monitoring method is provided. The hard disk system state monitoring method is to monitor the state of a hard disk system. The hard disk system comprises a backplane, an expander and a plurality of hard disks adapted in the device slots of the backplane. The hard disk system state monitoring method comprises the steps of: retrieving a logic and physical address mapping table from the expander; retrieving a physical address and device slot number mapping table; generating a logical address and device slot number mapping table according to the logic and physical address mapping table and physical address and device slot number mapping table; receiving a plurality of hard disk instant state signals; and establishing a hard disk system state database according to the logical address and device slot number mapping table and the hard disk instant state signals.