The changing mechanisms of air saturation in groundwater in different air travelling modes during surfactant-enhanced air sparging were investigated using a series of one-dimensional column experiments with the media of medium sand (025～050 mm) and gravel (5～10 mm) respectively. The results demonstrate that when air travels in the form of discrete channels, air saturation increases gradually with surface tension decreasing. When the surface tension is 495 mN/m, air saturation would not increase but slightly decreases instead. The decrease of capillary pressure caused by surface tension reduction is the main cause of increase of air saturation. When air travels in the form of bubbles, the air saturation improves gradually as the surfactant concentration decreases when the SDBS concentration is lower than 1 000 mg/L, and air saturation in porous media is directly affected by foam stability.