Abstract: The longitudinal joints of the segmental lining in pressurized water-conveyance tunnels are typically characterized by detailed configurations such as double-row bolts, multiple waterproofing measures, and edge gaps. Their flexural performance affects the overall mechanical response of the structure. To analyze the influence of detailed structural features on the flexural performance of the joint, this study constructs a joint flexural mechanical model, establishes the joint mechanical equilibrium equations based on the opening process, and validates against full-scale tests. The effects of the arrangements of bolts and waterproof grooves on the flexural performance of the joint are emphatically analyzed. The results show that the bending moment-rotation curve of the joint presents an S-shaped distribution. The flexural stiffness of the joint exhibits an overall nonlinear degradation trend as the joint opens. The presence of edge gaps reduces the initial flexural stiffness, while gap closure enhances the flexural performance. The ultimate flexural bearing capacity of the joint is optimal under a certain edge gap, with a more significant improvement under low axial force conditions. The double-row bolt arrangement significantly enhances the flexural performance on both sides of the joint. For example, under an axial force of 2 MN, the positive and negative ultimate bending moments are increased by 215.0% and 91.6%, respectively, compared with the boltless scheme; the positive ultimate bending moment is increased by 120.5% compared with the outer single-row bolt scheme, and the negative ultimate bending moment is increased by 67.9% compared with the inner single-row bolt scheme. Adjusting the bolts properly toward the segment edge can improve the same-side flexural performance.