Abstract: Lubrication plays a much important role for good working performance and long lifetime of rolling bearings. The distribution of lubricating oil layer out of the contact zone of ball-raceway directly determines the formation of lubricating film in the contact zone. In this paper, a rolling bearing model test rig was set up with a glass outer ring so that the oil layer distributed on the inner surface of the outer ring could be directly observed and measured by optical methods. This paper focused on exploring the influence of oil supply volume, speed and oil viscosity on the oil distribution and replenishment. The results show that both cavitation and reflow characteristics were affected by oil supply volume, speed and oil viscosity.