The study of the influence of waterswelling rubber block on waterproofing performance of composite sealing gasket of shield tunnel segment joint is of great significance. As a result, an optimum design method for composite sealing gasket based on geometric size and crosssection shape of waterswelling rubber block is proposed based on the second waterproof effect of waterswelling rubber block of composite sealing gasket. The method is used to analyze the numerical type selection of the universal composite sealing gasket with medium holes, and the influences of crosssection types and sizes of waterswelling rubber block on waterproofing performance of composite sealing gaskets are studied; and then the characteristics of waterproof properties and compressive properties of composite sealing gasket are obtained; finally, the optimum design of composite sealing gasket with medium holes is determined. The study results show that: (1) The secondary waterproof performance of composite sealing gasket can be improved by considering the waterproofing performance of waterswelling rubber. (2) Compared with the waterswelling rubber block with hexagonal crosssection, the waterswelling rubber block with trapezoid crosssection can greatly improve the waterproof performance of composite sealing gasket with medium holes. (3) The composite sealing gasket has obvious stage deformation characteristics during compression, i.e. when the deformation is small, the relation is linear, and with the increase of deformation, the relation is nonlinear.