The reinforcement mechanism of nano inclusions on the mechanical properties of nanocomposites is still a controversial issue. In this work, the polyethylene (PE) polymer nanocomposites were simulated by infusing different kinds of nano inclusions (bucky-ball, graphene, single-walled-carbon-nanotube (SWNT), X-shaped SWNT junction and Y-shaped SWNT junction) into PE matrices. The effects of these nano inclusions on structural and physical properties of PE matrices were considered through molecular dynamics (MD) simulations. The packaging densities of PE matrices were highly different from each other. The graphene inclusion had larger interaction with the PE matrix than the others. However, Y-shaped SWNT junction applied the strongest restriction on diffusion behaviors of PE matrices. Therefore, mean squared displacement of the PE matrix infused with Y-shaped SWNT junction is much smaller than that of pure PE. The effect of nano inclusions on primitive chain network of PE matrices was also considered. However, these nano inclusions did not significantly alter the underlying mesh of primitive chain network of PE matrices. The change of mechanical properties associated with these nano inclusions should be directly attributed to the interaction between polymer matrices and nano inclusions. (C) 2011 Elsevier Ltd. All rights reserved.