1. A block management method, for managing a plurality of physical blocks of a flash memory chip, the block management method comprising: grouping the physical blocks into a plurality of physical units; grouping a portion of the physical units into a data area and a spare area; configuring a plurality of logical units, wherein each of the logical units maps one of the physical units of the data area; grouping the logical units into a plurality of logical unit groups; configuring another portion of the physical units as a plurality of global random physical units corresponding to the logical unit groups, wherein each of the global random physical units corresponds to one of the logical unit groups; and getting at least one of the physical units as at least one global random substitute physical unit corresponding to one of the global random physical units.