Memory system having overwriting operation and therefore operation control method

The present invention discloses a memory system having an over-write operation, and operation control method thereof. The non-volatile memory device has a plurality of memory blocks including a plurality of memory cells stacked in the substrate normal to the direction. The reclaim necessity is determined based on the bit error level of the read data when the data of memory cells connected to the word lines of a selected memory block to be read. The memory cells are of the lead if the program is in a soft state data with the erased state of the memory cells connected to the word line is directly overwritten in the memory cells connected to the word line of the selected memory block.