A block management method for managing blocks of a flash memory storage device is provided. The flash memory storage device includes a flash memory controller. The block management method includes the following steps. At least a part of the blocks is grouped into a first partition and a second partition. Whether an authentication code exists is determined. When the authentication code exists, the blocks belonging to the first partition are provided for a host system to access, so the host system displays the first partition and hides the second partition. An authentication information is received from the host system. Whether the authentication information and the authentication code are identical is authenticated. When the authentication information and the authentication code are identical, the blocks belonging to the second partition are provided for the host system to access, so the host system displays the second partition and hides the first partition.