Abstract: In order to study the influence of cross-sectional deformation of large-diameter shield tunnel on the safety of tunnel structure in soft soil area, the development law of cross-sectional deformation and structural state caused by loading and unloading of large-diameter shield tunnel in Nansha deep and soft foundation section of Guangzhou 160 km/h operating urban rapid rail transit is studied by numerical simulation method. Results show that there is a high correlation between the cross-sectional deformation of the tunnel and the maximum opening of the joint, the stress of the joint bolt, and the damage of the concrete structure. The variation of tunnel arch waist diameter is taken as the control index, and the safety level of cross-sectional deformation of shield tunnel in urban rapid rail transit is established, which is divided into five levels: Ⅰ (normal), Ⅱ (degradation), Ⅲ (deterioration), Ⅳ (deterioration worsening), Ⅴ (danger). Corresponding treatment measures are put forward.