Abstract: A simulated galvanostatic occluded cell was used to investigate the effects of cathodic protection on chemical and electrochemical states inside occluded cells of localized corrosion for 1Cr13 and 0Cr18Ni9 stainless steels in 0. 5 mol/L NaCl solution. It was found that solution pH inside occluded cells increased from originally below the critical value to that above it,Cl-1 concentration of the occluded solution decreased by electromigration,and potential of the occluded alloy dropped from "corrosion" zone to "immunity" zone on the potential/ pH diagrams as the cathodic polarization was applied. The mechanism of cathodic protection to stifle pitting or cracking propagation could thus be interpreted.