Abstract: In order to study the influence factors of immiscible gas flooding oil recovery in fractured?vuggy reservoirs, the mechanism models of fractured?vuggy media are developed to analyze the influence of injection and production wells’reservoir type, vug distribution between injection well and production well, injection and production sites and gas injection rate on the EOR. The results show that the main mechanism of immiscible gas flooding is gravity drive due to the density differences between oil and gas, oil expansion and oil viscosity reduction to improve the flow ability. A better process could be gas injecting in fractured reservoir and high site, and oil producing in vuggy reservoir and low site. The existence of vugs could reduce the risk of gas channeling. The closer the vug to the top of reservoir and production well is, the higher the oil recovery will be. The oil recovery of gas flooding will increase and then decrease with the increase of gas flooding rate. The simulation results show that the oil recovery of gas flooding is mainly influenced by gravity, reservoir types, the distribution of vug between injection well and production well and gas injection parameters