The invention provides a 3D NAND memory device. The memory device comprises a substrate, a first memory region, a sub step region, run-through contact holes, and grid line gaps, wherein the first memory region is arranged on the substrate; the first memory region comprises a word line stacking layer and channel holes in the word line stacking layer; the side wall of the word line stacking layer adopts a step structure; the sub step region is arranged in the step structure; the sub step region is a stacked layer of an oxide layer and a nitride layer; the sub step region extends to the edge of the step structure in a word line direction; an insulating layer is arranged on the side wall, connected with the step structure, of the sub step region; the run-through contact holes are formed in the sub step region; and the grid line gaps are formed in the step structure outside the sub step region. By virtue of the run-through contact holes with the structure, connection between the memory device and a CMOS chip can be realized conveniently, and the memory device can be integrated with the existing process easily; particularly, when the thickness of the stacking layer is constantly increased, a step of etching metal stacking to form the run-through contact holes is not needed, so that realization of the process and constant improvement of the integration degree can be facilitated.