Flash memory device and program method thereof capable of preventing program disturb

A flash memory device and a program method thereof are provided to prevent program disturb to a memory cell adjacent to a selected memory cell, and to perform an accurate program operation without being influenced by a soft program or a punch-through phenomenon even when the gap between cells decreases and the length of a channel decreases. A voltage of corresponding channels is boosted by applying a pass voltage to a plurality of word lines including a selected word line. The channel voltage boosted by the pass voltage is discharged. A program voltage is applied to the selected word line. While the program voltage is applied, a local voltage is applied to at least one of the word lines where the pass voltage is applied. The local voltage is lower than the pass voltage and is equal to or higher than a ground voltage.