Abstract: The latest generation waterproof structural system for shield tunnel segment joints features a dual-channel waterproof groove, distinguishing it from previous designs where the waterproof grooves were arranged separately on both sides of the joint surface. The current design, with both grooves positioned on the outer side of the joint, is already being applied in practical engineering. Previous bending resistance calculation models for segment joints, based on the dual-channel waterproof groove configuration on both the inner and outer sides, did not consider the asymmetric nature of the cross-section, and the concrete material model used was relatively simple. This raises concerns about the suitability of directly applying these models to calculate the bending resistance of the outer dual-channel waterproof joints. To address this, the study introduces the centroid axis to characterize the asymmetric geometric properties of the joint surface and uses the concrete material model recommended in Appendix C of the current concrete structure design code to calculate the corresponding equivalent factors of the rectangular stress diagram. These factors were then incorporated into the derived bending resistance equation for shield tunnel joints, resulting in an improved calculation model. Furthermore, the improved model's adaptability and accuracy were discussed upon the bending tests of full-scale joints, and the influence of the waterproof groove layout on the joint's load-bearing capacity was analyzed. The results show that the accuracy of the bending resistance calculation for the outer dual-channel waterproof joints based on the model improved is significantly better than those of the existing model. For both inner and outer dual-channel waterproof joints, the accuracy of the models is similar under positive bending, but the model improved provides higher accuracy under negative bending. The change in waterproof groove design parameters has a strong nonlinear impact on the load-bearing capacity of the outer dual-channel waterproof joints, while it exhibits an approximately linear relationship for the inner and outer dual-channel waterproof joints. The improved model proposed provides an important reference for the safety assessment of the bending performance of shield tunnel joints and the for the design of joint configurations.