The invention discloses a forming method of a 3D NAND memory. The method comprises the steps of providing a semiconductor substrate, wherein a stacking structure is formed on the semiconductor substrate and comprises a plurality of sacrificial layers and isolation layers which are alternately stacked; the stacking structure is provided with a first channel hole and a second channel hole which communicate with each other, the second channel hole is aligned and deviated relative to the first channel hole, a step is formed at the junction of the first channel hole and the second channel hole, andthe first channel hole is filled with a sacrificial material layer; forming a side wall on the side wall of the second channel hole; etching the first channel hole to enable the width of the first channel hole to be widened and enable the width of the step to be reduced; forming charge storage layers on the side walls and the bottoms of the first channel hole and the second channel hole; forminga channel hole sacrificial layer on each charge storage layer; and sequentially etching the channel hole sacrificial layer and the charge storage layer on the bottom of the first channel hole to forman opening. The method provided by the invention prevents the charge storage layer at the step from being etched or damaged, thereby preventing the memory from failing.