In response to the problem of shields under-pass existing buildings, the interval of Nantong Metro Line 1 from East Huancheng Road Station to Intermediate People's Court Station under-passed the old residential area of Community Sendadi-Huayuan as the research object. Based on the site settlement monitoring data, an analysis of the impact of shield tunnel construction on the settlement of existing adjacent building foundations was conducted. Computational analysis of the shield tunnel under-pass this old residential area by numerical simulation, taked into account the upper building load and shield construction disturbance to the surrounding rock, The law of building foundation settlement was summarize. The results show that when shield machine tunneling in highly water-rich sandy soil and chalky soil, the head of the shield machine is prone to twist due to the disturbance of the ground and the dissipated of pore water, which causes instability in the excavation process and eventually causes surface settlement. And by setting a reasonable earth pressure value, keeping the balance of the digging surface, making the shield machine pass smoothly as much as possible, and at the same time doing a good job of grouting, filling the gap between the lining and the strata, can effectively reduce the surface settlement caused by the shield.