The glass transition temperature of polyethylene/graphene nanocomposites was investigated by molecular dynamic simulation. The specific volumes of three systems（polycthylene, polyethylene with a small graphene sheet and two small graphene sheets） were examined as a function of temperature. We found that the glass transition temperature decreases with increasing graphene. Then the van der Waals energy changes obviously with increasing graphene and the torsion energy also plays an important role in the glass transition of polymer. The radial distribution functions of the inter-molecular carbon atoms suggest the interaction between PE and graphene weakens with increasing graphene. These indicate that graphene can prompt the motion of chain segments of polymer and decrease the glass transition temperature （Tg） of polymer.
