In this study, the mixed lubrication of line contact is numerically calculated and analyzed. The surface asperities are in contact for mixed lubrication which differs from elastohydrodynamic lubrication. In this study, the Poiseuille term is neglected when the film thickness was smaller than the cut-off value about 0.5 nanometer, so that the surface asperities in contact or not contact can be solved in a system equation using the Newton-Raphson method. The mixed lubrication was studied in three parts, including the steady-state, the transient state and the start-up process. The effect of amplitude and wavelength on the film thickness and the pressure are investigated using the deterministic quantifiable method. The mixed lubrication zone in terms of rolling speed and load is established for the smooth surface under the steady-state conditions. For a single asperity on the surface, results show that the maximum pressure increases with increasing amplitude and decreasing wavelength. At high load situation, the film thickness is flattened around the asperity in the steady-state conditions, but it is increased due to the squeezing effect in transient state. For the start-up process, two surfaces are gradually separated due to the growth of film thickness, so that the contact area of two surfaces decreases linearly with time. However, the interval of contact time decreases with increasing roller speed and Young¡¦s modulus, but decreasing load.