Field experiments of domestic and overseas studies show that WAG flooding can further improve the oil recovery by 5%~10%. It can be used as an economical and effective way to improve oil recovery in the tertiary phase.With the help of laboratory displacement experiments,improved simulated cores,and setting up the experimental control group, a new experimental idea is put forward, and the mechanism of WAG flooding for enhancing oil recovery is revealed and clarified. The experimental results show that WAG flooding can slow the gas channeling and change the unfavorable water⁃oil ratio. Injecting⁃gas enhances the exchange, diffusion and imbibition of three⁃phase molecules. After alternating injection of water and gas, water drive seals high permeability zone, gas drive sweeps tiny pores along with the effect of gravity differentiation. The displacement process is a dynamic process in which the state of water binding in pores is broken constantly, and the large pores are plugged alternately. The breakthrough effect of injection gas on fluid is weakened, and the water absorption profile is improved, which prolongs the water breakthrough time of oil well and improves the oil recovery. For the reservoir with serious heterogeneity, the dynamic plugging effect produced by alternating water injection can further improve the oil displacement effect of WAG flooding.