Embodiments of staircase structures for three-dimensional (3D) memory devices double-sided routing are disclosed. In an example, a 3D memory device includes a substrate, a memory stack disposed above the substrate and including conductor/dielectric layer pairs stacked alternatingly, and an array of memory strings each extending vertically through an inner region of the memory stack. An outer region of the memory stack includes a first staircase structure disposed on the substrate and a second staircase structure disposed on the substrate. First edges of the conductor/dielectric layer pairs in the first staircase structure along a vertical direction away from the substrate are staggered laterally toward the array of memory strings. Second edges of the conductor/dielectric layer pairs in the second staircase structure along the vertical direction away from the substrate are staggered laterally away from the array of memory strings.