A garbage collection method is provided and applied to a data storage device. The garbage collection method includes the following steps: selecting source blocks from data blocks, wherein a total number of valid data of the source blocks is larger than or equal to a predetermined data number of a block; copying valid data of a part of the source blocks into a destination block, wherein a total number of the valid data of the part of the source blocks is smaller than the predetermined data number; copying all or a part of valid data of remaining source blocks into the destination block; updating a logical to physical addresses mapping table based on a mapping information of the destination block; and recovering all or a part of the source blocks as spare blocks.