In order to construct the highly stable foam for foam flooding，the influence mechanism of gas/liquid properties on foam stability was clarified from the perspective of liquid film permeability. The foam film permeability，foaming capability，elution half-life and foam half-life of seven foaming systems were evaluated using N₂ and CO₂ as gas medium by the bubble reduction method. The results showed that for the same gas，the more the number of hydrophobic carbon chains contained in the surfactant molecules，the stronger the interactions existed between surfactant molecules on the liquid film，and the smaller the foam liquid membrane permeability became. The liquid films permeability of CO₂ foam was 1—3 times as high as that of N₂ foams，so the stability of CO₂ foam was lower than that of N2 foam. There was a good correlation between the foam permeability and the foam half-life. As the liquid membrane permeability increased，the CO₂ foam half-life decreased rapidly.