An occluded corrosion cavity (OCC) simulated cell was designed，and electrochemical impedance spectroscopy (EIS) and polarization curves measurement were employed to study the effect of MoO42- on the development of underscale local corrosion of carbon steel in neutral NaCl solution.The results suggested that MoO42- could abate pH decrease and Cl- enrichment

and inhibit the auto-catalyzing acidification effect inside the OCC

so retard the development of underscale local corrosion obviously.The inhibition mechanism of MoO42- was that MoO42- transformed the hydrate ferrous oxide deposition film from anions selective to cations selective，and the cathodic process of underscale local corrosion was suppressed when it migrated into OCC.Meanwhile

the migrated MoO42- resulted in increasing the impedance of the film on the substrate metal and so inhibited the anodic process of the corrosion reaction inside the OCC.