Abstract: Based on the chloride ion diffusion characteristics, the time-varying corrosion patterns of prestressed segment pier and its seismic vulnerability during the whole life cycle are studied in this paper. On the basis of the research background of an offshore bridge structure, a prestressed segment pier with equivalent seismic capability is designed based on the original pier, and the numerical simulation is carried out using OpenSEES finite element software. The transport characteristics of chloride ion in the adhesive joint interface of precast segment bridge are applied to prestressed segment piers, and both uniform corrosion and pitting corrosion of various reinforcement materials are considered. The Pushover analysis method and incremental dynamic analysis method are used successively to calculate and evaluate the time-varying seismic performance and seismic demand of eroded prestressed segment piers. The results show that: firstly, the chloride ion transport characteristics in the joint interface zone change the time-varying corrosion state at different pier heights, resulting in uneven corrosion morphology along pier heights; secondly, considering uniform corrosion and pitting corrosion, the deterioration rate of the steel bar is obviously higher than that of the longitudinal bar inside the monolithic cast-in-place pier; finally, the seismic vulnerabilities of prestressed segment piers and monolithic cast-in-place piers present different characteristics during the whole life cycle of the bridge.