Abstract: This paper aims to understand the deformation characteristics of shield tunnel wall rock in soft soil. It builds a three-dimensional numerical model of every step of analyzing tunneling shield dynamic. The model is combined with the engineering example of one city subway shield tunnel under the existing bridge structure. The model is based on the consolidation finite element equation, Coulomb yield criterion and Darcy's law of pore water. It considers many factors that affect the quality of shield construction. The factors include cutter torque, propulsion, soil pressure, bridge foundation load, pore water pressure. The model is combined with triaxial experiments and field data. Issues in dynamic process of shield tunneling including the principle of modeling, the model rationality, the deformation characteristics of wall rock, and the safety of bridge structure, are studied in the model. The results show the follows. The process that shield tunneling affects the deformation of wall rock should be divided into three stages, approaching, passing through and leaving. When the shield tunneling approaches the section, the front surface appears arched under the influence of the cutter torque, propulsion and soil pressure when the shield tunneling approaches the section. When the shield passes through or leaves the section, the wall rock trends to settle, compress into the tunnel and compress forward, and the deformation is mainly at the top of the entrance to the hole, appearing agroove type. The calculated settlement of surface and abutment tallies with test results. The deformation of wall rock can meet the safety requirement of shield tunneling.