To investigate the influence of segmental lining width on ground and tunnel deformation during shield tunneling beneath residential buildings, a numerical analysis model was established using Midas GTS NX based on the engineering context of the Guangzhou Metro Guanggang Xincheng depot tunnel underpassing residential structures. The simulation results were validated through comparison with field monitoring data, and a gray relational analysis was employed to quantitatively assess the sensitivity of various deformation indicators to segment width. The findings indicate that, under the engineering scenario of a shield tunnel crossing beneath residential buildings, the use of 1.2 m-wide segments is more effective in controlling ground settlement and structural deformation of the tunnel compared with 1.5 m-wide segments. The deformation process associated with the 1.2 m segments exhibits a more stable settlement pattern, whereas the 1.5 m segments tend to induce repeated settlement–heave cycles in the surrounding ground, with a potential risk of segmental displacement exceeding warning thresholds. Sensitivity analysis shows that different deformation indicators respond unevenly to changes in segment width. From most to least sensitive, the indicators rank as follows: maximum ground deformation, maximum displacement during the post-excavation stage, and maximum displacement during the excavation stage. The results of this study provide theoretical support and reference for selecting segmental lining width in shield tunnels constructed beneath residential buildings.