The effect of the diameter of carbon nanotubes(CNTs)on the mechanical and tribological properties of nitrile-butadiene rubber(NBR)matrix was studied by molecular dynamics simulation.The mechanical properties of different composite models were investigated by constant strain method.The results show that the mechanical properties of the composites increase first and then decrease with the increase of the diameter of CNTs in NBR matrix.The shear simulation results show that the molecular chains in the matrix of the composites are broken to varying degrees after shearing,and the polymer molecular chains are aggregated to the friction interface.The molecular chains in the larger diameter CNTs reinforced NBR composites are relatively complete and continuous,resulting in better improvement of tribological properties.The larger diameter CNTs have a significant reinforcing effect on the NBR matrix,which limits the mobility of the NBR molecular chain.More molecular chains gather around CNTs,and the density and stability of the composite system are improved,thereby improving the mechanical and tribological properties of the CNTs/NBR composites.The diameter(6,6)CNTs reinforced NBR composites have higher shear modulus,excellent mechanical properties,and better friction and wear properties.