Abstract: In order to investigate the migration and distribution pattern of chloride ions in segment structure, and de? termine the impact of the factors such as external hydraulic pressure conditions, chloride ion concentration, pore water pressure and erosion time on the erosion pattern of lining segment, the Jiaozhou Bay 2nd subsea tunnel in Qingdao is used as an example in this study. The numerical model for chloride ions erosion and migration in lining segment in saturated and non-saturated conditions under the action of high hydraulic pressure is created by using the COMSOL Multiphysics? finite element platform. The structural mechanics module (solid), truss module (truss), porous media dilute substance transfer module (tds) and Richards equation module (dl) are used to simulate the chloride ions erosion pattern of segment model component under the coupling action of bending load, high hydraulic pressure and chloride ion concentration. As the results indicate: The convection of chloride ions in a segment component under the action of high hydraulic pressure is mainly controlled by the water head, while their diffusion is mainly affected by concentration gradient. The chloride ion concentration-depth curve can be divided into the convection segment,transition segment and diffusion segment.