Abstract: The passivity and pitting mechanisms of Fe-Cr alloys which contain 13%Cr, 17%Cr and 28%Cr in 3.5%NaCl solution have been presented by AES, EPMA technique and rotating disc-ring electrochemical measurement, especially, the behaviour of element Cr was investigated. By experiments and analysis, the following conclusions have been obtained:(a) The most important factor that control corrosion resistance of Fe-Cr alloys is the ratio Cr/Fe in passive film. (b) For diffenent Fe-Cr alloys, dissolution of Cr within pit is different. For alloys of Fe-13Cr and Fe-17Cr, dissolution of Cr follow dissolution-deposition reaction but following adsorption-desorption reaction is occurred for Fe-28Cr alloy.（c） Based on the experimental results and analytical discussion,models of pitting propagation mechanism for Fe-13Cr, Fe-17Cr alloys and for Fe-28Cr alloy have bene proposed respectively.