Abstract: Based on the excavation of deep foundation pit on the side of a underground station in Hangzhou, the reasons why the displacement of the underground structure exceeds the warning control value and the treatment measures are analyzed by means of three-dimensional numerical simulation and analysis of measured data.The results show that the excavation and unloading of foundation pit soil is an important factor affecting the displacement and deformation of the existing underground structure.The reasonable setting of foundation pit support stiffness is the key measure to control the increase of deformation.The deformation increment of foundation pit in soft soil area at the stage of dismantling support and backfilling cannot be ignored.The quality of enclosure construction is the decisive factor to ensure the safety of foundation pit and existing underground structure.The optimization control measures adopted in this project generally ensure the operation safety of adjacent subways, and provide a reference for the design and construction of similar projects.