Monolayer Graphene with extraordinary mechanical properties and super large specific surface area arouses extensive scientific interests as the potential reinforcement for fabrication of light-weight, high strength and stiffness metal-matrix composites. Previous experimental studies have demonstrated this reinforcement effect of graphene in a variety of metal matrix composites mainly in the shape of thin film or thick bulk, however, few talked about its reinforcement efficiency in the three-dimensional (3D) structure. Herein, to reveal the reinforcement effect of graphene in the 3D structure, a graphene-nickel composite foam has been fabricated through applying electrochemical co-deposition process. Specifically, a Polyurethane (PU) foam with the stochastic lattice structure is selected as the template, on which the graphene nano-flakes and nickel matrix were co-deposited through adjusting the electrochemical deposition conditions. Afterwards, the PU template was removed by a thermal decomposition process and the light-weight nickel foam in consist of hierarchy open cells and hollow triangle ligaments was obtained. Computational simulations and theoretical modeling were utilized to understand the underling mechanisms and provide a comparison to the experimental results. Our study on the 3D graphene-metal composite foam sheds light on fabricating novel high strength mechanical metamaterial.