Embodiments of 3D memory devices having zigzag slit structures and methods for forming the same are disclosed. In an example, a 3D memory device includes a substrate, a memory stack including interleaved conductive layers and dielectric layers above the substrate, an array of memory strings each extending vertically through the memory stack, and a plurality of slit structures laterally dividing the array of memory strings into a plurality of memory regions. Each of the plurality of slit structures extends vertically through the memory stack and extends laterally in a first zigzag pattern in a plan view.