A memory device including: a memory block including a plurality of cell strings; a peripheral circuit configured to set voltages for a program operation of selected memory cells in the cell strings, and program the selected memory cells by using the set voltages; and a control circuit configured to control the peripheral circuit so that the selected memory cells are programmed in response to a program command, and increase a channel voltage of non-selected cell strings including non-selected memory cells while the selected memory cells are programmed, and an operating method thereof.