A memory management method, a memory control circuit unit and a memory storage device are provided. In an exemplary embodiment, the memory management method includes: receiving a first write command and first write data and obtaining a first number; programming the first write data and moving first storage data stored in a plurality of first physical programming units, where a total number of the first physical programming units conforms to the first number; receiving a second write command and second write data and obtaining a second number; programming the second write data and moving second storage data stored in a plurality of second physical programming units, where a total number of the second physical programming units conforms to the second number; and erasing at least one physical erasing unit. Accordingly, waste of system resource in the data merging procedure may be reduced.