Hierarchical hybrid heterostructures are promising for efficient and sustainable electrocatalysts due to their various morphologies and outstanding electrochemical properties. Herein, heterostructured Cu_xO@NiCoS nanoarrays were in situ constructed on copper foam (denoted as Cu_xO@NiCoS/CF) and used as electrocatalysts for alkaline overall water splitting. Benefiting from the hierarchical hybrid heterostructure that exposes abundant active sites and the synergistic effect between Cu_xO and NiCoS, Cu_xO@NiCoS/CF shows better electrocatalytic performance than single-component electrocatalysts (Cu_xO/CF and NiCoS/CF). The influence of the initial metal source ratio (Ni/Co) during the electrodeposition on electrocatalytic performance was further investigated. Impressively, the optimized Cu_xO@NiCoS-1/CF exhibits a small overpotential of 110 mV at 10 mA cm⁻² for the hydrogen evolution reaction (HER) and 313 mV at 30 mA cm⁻² for the oxygen evolution reaction (OER). Moreover, Cu_xO@NiCoS-1/CF as bifunctional electrocatalysts reach a current density of 30 mA cm⁻² at a low cell voltage of 1.79 V and display remarkable electrocatalytic durability in an alkaline solution. This work can provide a new idea for designing and preparing novel non-noble metal electrocatalysts with the benefit of structural diversity.