A block erase method for a flash memory is provided. The block erase method is to perform block erase on a block with a predetermined block size. The block erase method includes: performing an erase verification on bytes byte-by-byte in the block when performing the block erase; checking an erase step of the byte when the byte does not pass the erase verification; when the erase step of the byte exceeds a predetermined threshold value, performing the block erase with a partitioned block smaller than the predetermined block size, and returning to an erase verification stage to perform the erase verification; and when the erase step of the bytes does not exceed the predetermined threshold value, continuing to perform the block erase with the predetermined block size, and returning to the erasure verification stage to continue to perform the erase verification.