In order to evaluate the waterproof performance of the shield tunnel joint under the conditions that opening amount and dislocation exceed the design allowance, the limited opening amount and dislocation displacement of shield tunnel are discussed so as to meet the waterproof requirements. And then two kinds of gaskets are selected to carry out waterproof test under the conditions of extreme opening amount and extreme dislocation displacement based on the Nanjing Heyan Road Tunnel Project. The variation rules of the gasket waterproof performance under the conditions that opening amount and dislocation exceed the design allowance are obtained as follows: (1) The waterproof performance of the gasket decreases gradually with the increase of the opening amount, and the decreasing range increases gradually with the increase of the opening amount. (2) With the increase of the dislocation displacement, the waterproof performance of the gasket shows a general trend of decreasing by fluctuation until it reaches a critical value, after the dislocation displacement exceeds the critical value, its waterproof performance will rapidly decrease until it fails. For underwater shield tunnels with a risk of opening amount and dislocation displacement exceeding the designed values, it is recommended to consider its waterproof performance under extreme conditions in the design.