To clarify the global circumferential force boundary and its evolution in prestressed double-layer linings of shield water conveyance tunnels under high internal water pressure during the prestressing–operation process, an analytical model was developed based on double-layer thick-walled cylinder theory. The model considers prestressing action, internal water pressure, and interlayer displacement compatibility. Closed-form expressions were derived for the circumferential stress, radial displacement, and equivalent interfacial reaction of the prestressed lining and segmental lining, and analytical criteria were further proposed for the stress-transition pressure and critical internal water pressure. The model was validated using prototype test data and numerical results from the Pearl River Delta Water Resources Allocation Project. The effects of prestress level and thickness ratio on the circumferential mechanical response and critical internal water pressure were then analyzed. The results show that, during the prestressing stage, prestress first establishes a circumferential compressive stress reserve in the inner prestressed lining and then affects the initial stress state of the outer segmental lining through interlayer displacement compatibility. During the operation stage, as the internal water pressure increases, the compressive stress reserve in the prestressed lining is gradually weakened, and the global structural state successively evolves through three stages: compressive-stress-reserve domination, stress-transition, and crack-control critical state. The analytical results agree well with the prototype test and numerical results, indicating that the proposed model can reasonably capture the evolution trend of the global circumferential force boundary of the prestressed double-layer lining. The parametric analysis indicates that the prestress level is the dominant factor controlling the initial compressive stress reserve during prestressing, the force boundary position during operation, and the critical internal water pressure. In contrast, the thickness ratio mainly plays an auxiliary role in adjusting the critical boundary by regulating the bearing capacity and stress reserve of the inner lining. The proposed method provides a theoretical basis for rapid mechanical analysis and key parameter selection of prestressed double-layer linings under high internal water pressure.