Abstract: The uncertainty in the time-variant probability model of a reinforcement sectional area is generated by the limited current information and unknown future condition. The uncertainty of influencing factors on reinforcement corrosion under the chloride ion environment is summed up fuzziness and randomness in the reinforced concrete bridges. The Mont Carlo interval numerical simulation technology is incorporated, and both the uniform and local corrosion states are considered. The fuzzy probabilistic characteristic of corrosion initiation time is analyzed. The sectional area mean and standard deviation functions including time and threshold values are established. The fuzzy probabilistic characteristic of corrosion pit depth at the different time under local corrosion environment is analyzed. The sectional area means and standard deviations under two corrosion states are compared, respectively. The results show that the effect of uncertainty of influencing factors of corrosion on the reinforcement sectional area model is significant. The discreteness of sectional area degradation under local corrosion is remarkable. Therefore, the sectional area model under local corrosion is suitable for the time-variant reliability analysis of a concrete bridge.