Abstract: The hydrological and geological conditions of Qiantang River estuary are very complicated. The foundation pits along it are threatened by floods and strong tides. Based on the intensive investigations of projects, seawalls and typical geological cross sections of Hangzhou reach of Qiangtang River are selected to conduct numerical studies on the effects of high tidal level and design flood level of Qiangtang River, distance of pit from the river, reinforcement of the pit bottom, excavation depth and insertion depth of enclosure walls on the bebaviors of the alluvial silt foundation pits. The results reveal that (1) the silt pits along the river undergo large deformations under the effects of water levels, (2) the improvement by the reinforcement of pit bottoms is noticeable, (3) the seepage at the bottom of the enclosure structures for the silt pits is fast and the flows are concentrated, thus measures should be taken to lower the water head differences between the inside and the outside of the pits, and when cut-off walls leak, emergency countermeasures should be taken. The numerical results offer references for engineering design.