In order to clarify the reaction essential of electrochemical repairing method, which was developed to repair the passive film on pits and suppress pitting corrosion on passive 18-8 stainless steel (18-8ss) after occurrence of pitting, the electrochemical characteristics, morphology and composition of passive film after different treatments were investigated by electrochemical impedance spectroscopy (EIS), Cyclic Voltammogram (CV), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The dynamic behavior of reactions occurred at lower potential (E-L = - 200 mV) and higher potential (E-H = 1000 mV) of alternating electric filed was discussed respectively and the correlation between those reactions was analyzed. Based on above results, reaction essence of electrochemical repairing for pitted 18-8ss electrode was proposed: during the periodic action of alternating current, recycle reactions take place on the surface and the pit area of pitted electrode, i. e., metal dissolves into cations (occurs at E-L) and form hydrous hydroxide, the hydrous hydroxide turns into metal oxide ( occurs at E-H), a 'bipolar mode' passive film forms and Cr content is increased in repaired passive film. At the pit area, enclosed state of the pit is destroyed by the perturbing effect of alternating current in 1.0 M H2SO4 solution, thus the pit area will be repaired through above-mentioned process. (C) 2005 Springer Science + Business Media, Inc.