Abstract: Unloading and water head difference between the inside and outside of a foundation pit would induce seepage in high water table ground,which had significant influence on excavation engineering.Based on the unsteady seepage theory,analytical formulas for calculating the water head in active and passive zones of a foundation pit were obtained under the assumption that groundwater seepage was one-dimensional.Variations of water head with time in active and passive zones were analyzed,and the influence of water head variation on pore water pressure,earth pressure and lateral pressure acting on retaining structure was further investigated.