A memory system includes a plurality of blocks of memory blocks, each including a plurality of memory cells. The method for programming the memory system includes during a program process, performing a first program operation to program a first memory block, waiting for a delay time after the first program operation is completed, after waiting for the delay time, performing an all-level threshold voltage test to determine if threshold voltages of the first memory block are greater than corresponding threshold voltages, and performing a second program operation to program the first memory block according to a result of the all-level threshold voltage test.