A series of 3D numerical simulation about the shield tunnel undercrossing existing building was accomplished.Results show that important parameters include relative position of tunnel and existing building,weight and stiffness and geometric form of existing building have dominating influence on the pattern of surface settlement trough,especially in changing the maximum settlement and modifying the width and form of settlement trough.Based on the Shanghai Metro Line 11 undercrossing the historic buildingXujiahui Observatory,full threedimensional model about shield tunnel undercrossing Xujiahui Observatory was established to simulate construction process.Settlements of surface were forecasted.Measuring points were arranged to monitor surface settlements during undercrossing to verify simulation results.