Grain size dependent strength,known as Hall-Petch relation,has been approved to be valid in crystalline metals and alloys.However,softening would eventually occur as grain size reduced into nanoscale that below a critical value.Hence,it is essential to find a way to break the strength limitation by avoiding the deformation mechanism transition from dislocation-mediated to grain-boundary-mediated processes.By replacing grain boundary (GB) of nanocrystalline Cu with graphene,in the present study,molecular dynamics simulations show that graphene-boundary (GrB) embedded GrB/Cu nanocomposites exhibit enhanced enlarged Hall-Petch slope with decreasing grain size.The absence ofinverse-Hall-Petch relation and the extremely high strength derived at the GrB/Cu nanocomposites were interpreted by the high back stress and abundant dislocation activity that attributed from the high-degree of heterogeneous structure of the nanocomposites.