Memory management method, memory storage device and memory control circuit unit

The invention provides a memory management method, a memory storage device and a memory control circuit unit. The memory management method comprises the following steps: dividing a plurality of non-idle entity erasing units into a first entity erasing unit and a second entity erasing unit, wherein the data updating frequency of the first entity erasing unit is lower than the data updating frequency of the second entity erasing unit; selecting a third entity erasing unit from the entity erasing units which belong to the first entity erasing unit; extracting a fourth entity erasing unit from idle entity erasing units, and copying valid data stored in the third entity erasing unit into the fourth entity erasing unit; and erasing the third entity erasing unit.