Abstract: To analyze the oil transport controlled by oil-control-ring, a 4-stroke internal combustion engine is investigated in this paper. Based on the structural characteristics of the oil-control-ring and the oil layout on the cylinder surface, the equation of force balance and the lubricant oil flow equilibrium are established so as to study the oil transport process, the change of lubricating oil quantity in the ring bank area above the oil ring, and its bottom-up delivery process along the cylinder liner during operation. The result shows that the oil-control-ring governs the transport; Oil accumulates in the third land during the down-stroke while in the up-stroke, oil is transported to the top dead center to keep the piston be well lubricated around the top dead center.