The study on waterproof failure mode of shield tunnel, failure mode of sealing gasket and improvement technologies is of great significance. Firstly, the macroscopic morphology of the leakage of shield tunnel under construction is analyzed based on the statistical data. And then 2D model is established by ABAQUS software, and the average contact pressure is taken as the evaluation index to analyze the failure mode of sealing gasket of shield tunnel segment under unfavorable working conditions. Finally, improving methods for the waterproofing performance of the sealing gasket are studied based on rubber hardness parameters and gasket hole parameter. Some main conclusions are drawn as follow: (1) The segment joint leakage is the main leakage mode for staggered joint shield tunnel, which mostly occurs in Tjoint. (2) The opening and the outer opening angle of the segment affect the waterproof performance of sealing gasket, and leakage mostly occurs on contact face between sealing gaskets. (3) The average contact pressure between gaskets is linearly positively correlated with the rubber hardness; and according to the average contact pressure between gaskets, the effect of adjusting the closed holes is the best.