Program method of nand flash memory device

The present invention relates to a program method of the NAND flash memory device. Program method of the NAND flash memory device according to the present invention operates as a separate cache memory by loading the data to the page buffer of the second mat while the program operation is performed on the first mat. A program method of the NAND flash memory device according to the present invention performs a page buffer and loading all the data to the page buffer, then the program operation at the same time for the first and second mat in the second mat of the first mat do. According to the program method of the NAND flash memory device according to the present invention, it is possible to reduce the program time.