A three-dimensional composite of Co3O4 nanoparticles and nitrogen-doped reduced graphene oxide (3D Co3O4/N-rGO) with a unique 3D porous structure was prepared, and its catalytic activity in lignin model compound oxidation was explored. The 3D Co3O4/N-rGO composite exhibits improved catalytic performance as compared to Co3O4 nanoparticles or 3D N-rGO in the oxidation of lignin model compounds. The higher catalytic activity of the 3D Co3O4/N-rGO composite is attributed to the combination of its porous structural features, large surface area that is provided by the 3D N-rGO matrix, and active Co3O4 nanoparticles doped on the N-rGO surface. The structural features of the 3D Co3O4/N-rGO are beneficial to reactant and product diffusion and transportation, and also are helpful in preventing aggregation of Co3O4 nanoparticles. In addition, the introduction of N atoms in rGO is also favorable for the formation of active oxygen species for the oxidation of model compounds. Given the high activity and the easy recovery from the reaction system, the 3D Co3O4/N-rGO composite should be applicable to non-noble metal catalytic systems for lignin model compounds.