In order to explore the effect of tidal action on the ring joints opening and waterproof property of the large section shield tunnel, large section subsea shield tunnel, namely, Su’ai Channel project built in region with significant changes in tides is based on. The equivalent flexural rigidity of the longitudinal joint is calculated by establishing the ANSYS finite element entity model. The longitudinal equivalent stiffness model of the tunnel is established, and the longitudinal bending moment and axial force’s distribution of the tunnel under tidal load is obtained by applying the head pressure corresponding to the difference of tide level. Then, opening of the ring joint at each position along the longitudinal direction of the shield tunnel was determined by calculation formula of opening of the ring seam. The research results show that: the larger opening of ring joint occur in the locations where the hardness and softness of strata change dramatically along the longitudinal direction. Due to uneven longitudinal settlement at these location, the results of bending moment and axial force tend to be large, which affect the opening of ring joint. The maximum ring joint opening caused by tidal loads is 0.271 mm, which has a low impact on the waterproof property of joints. 