The deformation of the foundation pit and adjacent pipelines under the excavation and dewatering is discussed by FEM based on a deep foundation pit project in Hangzhou, in which the soil constitutive model is HSS model. The simulation results are in good agreement with field monitoring results, which verifies the rationality of the selection of calculation model and parameter. Based on the simulation, the optimization scheme of dewatering is put forward while the waterproof curtain cut off the hydraulic connection inside and outside the foundation pit, and the deformation response of foundation pit and adjacent pipelines with different insertion depth of the waterproof curtain is studied under steady seepage. The results show that: as the depth of the suspended waterproof curtain increases, the ground water head difference between the inside and outside of the pit increases linearly, the peak value of the lateral displacement of the retaining structure increases linearly, and the vertical displacement of the pipeline and the surface settlement outside the pit decrease linearly; compared with the suspended waterproof curtain, the waterproof curtain which goes deep into impermeable layer has significant advantages in controlling the surface settlement outside the pit and the deformation of the adjacent pipeline caused by dewatering, but for the control of the retaining structure deformation is more disadvantageous.