In this paper,a nonlinear numerical model of bearing capacity for quasi-rectangular shield tunnel structure is established. In the model, the material nonlinearity, the geometric nonlinearity are all taken into consideration. Three groups of test structrures under limit working condition are simulated numerically. The results of the numerical simulation and full-scale ring tests are compared to verify the correctness and effectiveness of the model. Then the key parameters are analyzed to investigate the mechanical behavior of the structure. The results show that the failure of the structure originates from the failure of longitudinal joints,and eventually the structrure reaches the ultimate bearing capacity due to the failure of T block. According to the numerical analysis, the structural failure mode is related to the mechanical properties of longitudinal joints, segments and interior column. The ideal failure mode of the structure is that the bearing capacity of longitudinal joints is fully utilized, while the reinforcement of segment is yielded which leads to the ductile failure mode of the structure.