Water control is an effective method to enhance the oil recovery in the high water-cut reservoir. It is proved that the water production can be reduced by the entrapped gas in the oil field. But the mechanism is not well studied. In this paper, the mechanism of enhanced oil recovery by entrapped gas is studied by experiments and numerical simulation. Based on the core flooding tests and simulation study, the increments of oil recovery caused by entrapped gas are 8% and 2%, respectively. After the gas is entrapped in the core sample, the water relative permeability is decreased by 10.5% and the oil relative permeability is only decreased by 3.5%, which proved that the entrapped gas has a dramatic effect on blocking water phase. The more gas is entrapped, the more oil is produced. Different methods to achieve entrapped gas are also discussed, simultaneous water, and gas injection is a preferred entrapped gas formation method than gas injection method and water alternating gas injection method. Under the immiscible condition, the entrapped methane has a better performance on enhancing oil recovery than the entrapped nitrogen. [ABSTRACT FROM AUTHOR]