Abstract: Alternating immersion test was applied to 2024T3 Al alloy. Electrochemistry Impedance Spectroscopy (EIS) by time domain method was performed on the specimens. Statistic method was also used to deal with data because localized corrosion is a stochastic phenomenon. The results show that the reciprocal of low frequency impedance (1/R_d) was consistent with the Gumbel distribution law. The dynamic variation curve of 1/R_d vs. test period was somewhat of S shape which must be divided into two stages to treat the data, i.e. pitting and intergranular corrosion (Sigmoidal curve) and exfoliation (linear line). Compared with the maximum corrosion depth data (d_m) measured by optical microscope, it can be concluded that 1/R_d and d_m have similar statistical distribution and time-dependent growth. Quantitative relation between the 1/R_d and d_m has been established. According to the relation, EIS by time domain method can enable a nondestructive, quantitative and quick evaluation for localized corrosion of 2024 Al alloy.