We investigate flow and slip behaviour of Santotrac 50 molecules under high shear in Couette cell by means of Molecular Dynamic simulation to understand reduced friction force. Molecular chain stretches and oriented to shear direction, and move. Slip starts on metal surface at 2 Â 10 8 s À1 , and increases with shear rate. Slip length keeps scale at nanometre. Molecular conformation and occurrence of slip both indicate a reduced shear stress. Furthermore, when changing wettability, slip length increases in power law and thus decreases shear stress greatly. Occurrence of low-density region near surface can explain slip. And thus, we extended apparent slip model, which divided lubricant into liquid layers with different viscosities, to elucidate the relationship between molecule distribution inner layer and slip on surface influenced by shear velocity and wettability. Above all, our research sheds light on flow and slip behaviour of complex fluid and can be applied in improving lubrication property.