In order to explore the change of elastohydrodynamic lubrication(EHL) oil film under zero entrainment velocity(ZEV) in a loading process,friction experiment with PAO100 lubricating oil was carried out using a ball-disk optical interference testing rig.During the experiment,the servo motor drives the steel ball and sapphire disc to rotate reversely at equal speed,and the contact was loaded linearly.The oil film images between the ball and disk were captured by an industrial camera,and the oil film thickness at the middle section of the contact in the entraining direction after the experiment was measured by a dichromatic interference intensity modulation(DIIM) software.The results show that the regularity of oil film is not strong when the surface speed is relatively low and the load is relatively small under the loading condition.Only when the load increases to a certain value,the “temperature-viscosity wedge” effect starts to play a role and a centralized dimple is formed.The occurrence of the centralized dimple becomes earlier when the surface speed is increased.Under the condition of higher speed,the small centralized dimple rapidly evolves into a large dimple.The comparison with the steady-state results shows that the transient effect holds back the effect of “temperature-viscosity wedge”.