The theoretical model is suggested which describes micromechanisms of plastic deformation in bimodal metal-graphene composite consisting of large grains embedded into nanocrystalline/ultrafine-grained metal-matrix reinforced by graphene inclusions. In the framework of the model, lattice dislocation slip and grain boundary sliding has occurred in nanocrystalline/ultrafine-grained matrix, and lattice dislocation slip and migration of twin boundaries are realized in large grains with a nanotwinned structure providing the plastic deformation of bimodal metal-graphene composite. With this assumption, the yield stress of nanotwinned bimodal metal-graphene composite was calculated.