Phreatic and confined water always are major objects for engineering dewatering in foundation pit excavation, but the groundwater in aeration zone is usually being neglected. The practice proved that the influence of the groundwater in aeration zone should be paid enough attention. By the analysis, the influence of aeration zone in low cohesive soil on foundation pit engineering was discussed in this paper, and an improved method of light well-point dewatering was put forward to drain perched water with low cost and good effect.