Research conclusions:As the water reduction engineering is strong in speciality and obvious in territoriality，the similar experience is very important. There are deeply complex Quaternary loose sediments distributed along Qiantang River, where multilayer thickness of pore confined aquifer is well developed. Strong hydraulic connection is dominated between aquifers，forming a complex aquifer system. Because high pressure water level is existence，it greatly increased the difficulty of dewatering of deep foundation pit. In order to ensure rationality and validity of a dewatering design，the dewatering design must consider engineering geological conditions，hydraulic geological conditions and foundation bracing systems to select reasonable hydrological parameters and make analysis of seepage flow seepage mode. The dewatering should be conducted strictly according to the dewatering design dewatering subsidence and dynamic control to reduce the watering depth of pressure-bearing water for with three-dimensional scheme with immediate effective controlling the around the foundation pit as practice，the method is correct，reliable much and as possible to is a mean ensure the safety of surrounding buildings. to design the dewatering of deep foundation pit ,where deeply complex Quaternary loose sediments exist.