In order to study the influence of axial force of concrete segment of shield tunnel on ultimate bending moment of segment joint, the concrete segment joint strengthened by straight bolts is simplified as a beam model; and then the computing model for ultimate flexural capacity of reinforced concrete segment is proposed. The equations for force equilibrium and moment equilibrium of segment joint crosssection are derived; and the relationship between bolt stress in tensile zone and ultimate strain of concrete and that between height of compression zone and the ultimate strain of concrete are established based on assumption of plane deformation of segment crossssection under the action of bending moment. In case studies, the influence of axial force of concrete segment on ultimate bearing capacity of concrete segment and the broken modes of segment joints are studied. The study results show that the ultimate bearing capacity of segment joint increases with axial force of segment increases. The feasibility of the proposed computing model is verified by comparison between the study results and finite element simulation results.