Embodiments of through array contact structures of a 3D memory device and fabricating method thereof are disclosed. The memory device includes an alternating layer stack disposed on a first substrate. The alternating layer stack includes a first region including an alternating dielectric stack, and a second region including an alternating conductor/dielectric stack. The memory device further comprises a barrier structure including two parallel barrier walls extending vertically through the alternating layer stack and laterally along a word line direction to laterally separate the first region from the second region. The memory device further comprises a plurality of through array contacts in the first region, each through array contact extending vertically through the alternating dielectric stack.