Molecular dynamics simulation is an effective method to evaluate material properties at the early stage of material design, which can accurately guide the design of new materials and shorten the material development cycle. Therefore, in this study, the changes of tribological and mechanical properties of graphene reinforced polyethylene (PE) composites during friction process were simulated by molecular dynamics. The analysis results showed that the graphene induced the formation of a transfer film consisting of PE molecular chains at the friction interface, thereby reducing the interaction between the friction pair and the composites and preventing numerous molecular chains from collecting at the friction interface. Meanwhile, the graphene enhanced the free-volume fraction to strengthen the mechanical properties of the composites-thereby producing high-performance composites. Thus, an appropriate graphene content could notably reduce both the coefficient of friction and wear rate of PE, and reinforce the polymer's tribological and mechanical properties. By adding 2 wt.% of graphene, the mechanical properties of the composite were significantly improved, while the coefficient of friction decreased by 29.6% and the wear rate decreased by 89.9% compared to that of pure PE, and presented the best strengthening effect. This knowledge will be useful for future designing and developing composite polymer materials with excellent tribological and mechanical properties used for key moving components.