The invention provides a vertical memory device and a preparation method thereof. The device comprises a lower logic unit and an upper logic unit, and the upper logic unit is located above the lower logic unit and makes contact with the lower logic unit; the lower logic unit comprises a substrate and a first gate structure layer, a first source region, a first drain region and a first channel region are formed in the substrate, the first channel region is located between the first source region and the first drain region and is adjacent to the first source region and the first drain region, and the first gate structure layer is located on the upper surface of the first channel region; and the upper logic unit comprises a second source region, a second drain region, a second channel region and a second gate structure layer, the second source region, the second drain region, the second channel region and the second gate structure layer are sequentially stacked above the first gate structure layer, the second gate structure layer comprises a second gate dielectric layer and a second gate metal layer, and the second gate dielectric layer is wound in the circumferential direction of the second channel region, the second gate metal layer is wound on the circumference of the second gate dielectric layer, and the drain electrode of the upper logic unit is used as a capacitor of the lower logic unit at the same time. According to the vertical memory device and the preparation method thereof of the invention, dynamic charge refresh time can be reduced.