Abstract: Based on monitoring chloride ion's induction period by comsol, this paper analyzes the major factors affecting the induction period of chloride ions, including chloride ions diffusion coefficient, protective layer thickness and chloride ions concentration. The actual affecting model is established by selecting different water-cement ratios, different thickness of the protective layer and chlorine ions concentration. Simulation results show that favorable induction period can be obtained with the following parameters: water cement ratio of 0.28~0.38, and protective layer thickness of 60~80 mm. The monitor model is applied to predict the induction period of the piers of a sea bridge. Suggestions are put forward based on the monitoring results.