In order to study the mechanism of improving the boundary lubrication performance n-octane by nano ZnO,by considering boundary roughness,a molecular dynamics boundary lubrication model with convex peaks was established.The density distribution and radial distribution function of base liquid and ZnO nano-fluid under a loading condition of 25 MPa to 400 MPa,and the friction characteristics of the base liquid and ZnO nano-fluid under different positive pressures were analyzed.The results show that the density layers occur in both base liquid and nano-fluid under different positive pressures,the greater the positive pressure,the more obvious the layering.The addition of nano ZnO will change the structure of the base liquid and enhance its bearing capacity.Nano-fluids can reduce the stress and strain of friction surface and reduce the degree of lattice distortion during shearing.The friction coefficient of the interface model of the nano-fluid with a mass fraction of 1.636% ZnO is 0.078 1,which is reduced by 47.4% compared with the interface model of base liquid interface,indicating that nano ZnO has a significant friction reducing effect on the n-octane boundary lubrication interface.