Abstract: The design of Zhanjiang Bay Tunnel, a representative sea-crossing shield tunnel in China, is faced with several challenges including high hydraulic pressure, long distance, and durability of its segmented lining in submarine environment. This paper describes optimal designs of the lining structure of this tunnel. During its construction period, the deformation and stress response in the circumferential rebars and the tunnel segments were monitored in-situ to observe the mechanical behaviors of its lining structure under high water pressure. A detailed three-dimensional finite element modeling is developed to investigate the static behaviors of the entire segmented ring in different conditions of external water pressure and lateral coefficient of earth pressure. The results show that: (1) the stress development of reinforcement in the segmented ring can be divided into four stages and the most significant fluctuations in the rebar stress occur in the initial stage following the completion of segment assembling. (2) Both the measurements and simulations indicate that this ring structure is in a state of overall compression under high external water pressure. (3) A linear relationship between its transverse deformation and external water pressure is observed and it is greatly influenced by the lateral coefficient of earth pressure. With water pressure increasing, the deformation pattern is transformed from horizontal oval to overall inward compression. (4) In stiff strata, an increase in water pressure mitigates the tendency toward horizontal oval, while in soft strata, it aggravates overall compression of the segmented ring.