Pit excavation will cause deformation of the shield tube sheet, but there are fewer studies related to the refinement model of shield tunnel under the consideration of peripheral pressure. Based on the formula for calculating the additional peripheral pressure of tunnel lining, the article establishes a refined model of a three-ring shield tubular sheet in combination with practical cases, carries out structural calculation and analysis, and compares the calculated values of tunnel deformation with the measured values to verify the reliability of the model in this paper. Ellipticity and standard deformation control values are used as indicators to assess the tunnel’s safety condition. The influence law of pit excavation and unloading on the tunnel is studied. The results show that: In the process of foundation pit excavation, tunnel segments gradually change from soil unloading control under the tunnel to unloading control caused by foundation pit excavation, and the horizontal displacement gradually increases. Under the same excavation schedule, the vertical displacement at the top of the tunnel changes more than that at the bottom; the stress at the joints between the tube pieces is larger, the maximum stress of concrete occurs in the connection place of the standard block, and the maximum stress of bolts occurs in the connection place of the bolts between the rings; the clear distance of the tunnel from the bottom of the foundation pit is larger than that between the tunnel pieces. The larger the clear distance of the tunnel from the bottom of the pit, the smaller the displacement at the top of the tunnel and the larger the displacement at the bottom, and the horizontal displacement gradually increases; the deformation and ellipticity of the tunnel are strictly controlled in the process of excavation of the pit, and the deformation and ellipticity of the tunnel will gradually exceed the control value if the excavation is continued after the pit is finished.