Three-dimensional (3D) hierarchical nanostructure consisting of vertically-aligned Co₃O₄ nanowires and Co(OH)₂ nanosheets have been successfully prepared by a two-step wet chemical method. In this structure, the Co₃O₄ nanowires were wrapped and interconnected with ultrathin Co(OH)₂ nanosheets and combined into a whole network. The Co₃O₄/Co(OH)₂ 3D network nanostructure shows a high specific capacitance of 867 F/g at a current density of 2 A/g, and a satisfied cycling stability with 84.5% capacitance retention after 5000 cycles. An asymmetric supercapacitor with the Co₃O₄/Co(OH)₂ and activated carbon was also assembled by using 2 M KOH as electrolyte. The supercapacitor shows a wide potential window of 0-1.5 V, and the energy density can reach 25.6 W h kg^-1 at a power density of 939.03 W kg^-1. Our work has proposed a new strategy to improve the electrode performance of electrochemical supercapacitors by rationally building three-dimensional nanomaterial network with nanowires and nanosheets.