The present disclosure provides a redundancy method for a flash memory device. The flash memory device comprises multiple storage areas in which at least one storage area is configured as a temporary storage area for redundant operations. The method comprises: performing redundant operations to a first set of pages stored in one of the plurality of storage areas in a cache to generate an intermediate result; storing the intermediate result to the storage area of the at least one temporary storage area for redundant operation from the cache; performing redundant operations to the (m+1)th set of pages stored in one storage area the redundant operation result of and the first set of pages stored in the at least one temporary storage area for redundant operation to produce a final result in the cache; storing the final result to the corresponding pages in the (m+1)th set of pages from the cache.