In the paper, numerical simulation study is made on the waterproof failure mechanism of elastic sealing gaskets by means of ABAQUS program, with the design of the waterproof system of an underwater shieldbored tunnel as example. The finite element model used in the paper is compared with the previous simplified model, and the waterproof failure mechanism of elastic sealing gaskets in the case of joint opening and that in the case of joint staggering are analyzed respectively. Conclusions drawn are as follows: 1) In the case of joint opening, the water leakage mainly occurs at the contact surface between the sealing gaskets; 2) In the case of joint staggering, the water leakage at the contact surface between the sealing gaskets turns into water leakage at the contact surface between the sealing gasket and the concrete segment as the staggering displacement grows. 