Five pretreatment methods were used to prepare the surface of galvanizd steels then painted with epoxy resin respectively. The coated specimens were tested in 3.5wt% NaCl solution by Electrochemical Impedance Spectroscopy (EIS) for 21 days totally. EIS results showed that the protection mechanism of the paint films was mainly due to their insulating and capacitance effects in the beginning. However, the paint films were degraded gradually as the immersion time increased. In addition, EIS also showed that corrosion reactions at the paint films/substrate interface were diffusion controlled except for those treated with eash primer.