Nanocrystallized bulk 304 stainless steel（304ss） was prepared by the severe rolling equipment. X- ray diffraction （XRD）, optical micrograph and transmission electron microscopy （TEM） were used to characterize micro - structure of materials. Meanwhile, using different electrochemical methods, such as polarization curves, electrochemical impedance spectrum （ EIS）, and Mott - Schottky analysis, the effect of chloride ion attack on the passive film was investigated in 0.05 mol/L H2SO4 ＋0.05 mol/L NaC1 aqueous solution. The passive film formed on surface of nanocrystallized bulk 304ss was more compact and more protective to chloride ion than that formed on its counterpart alloy. Meanwhile, the donor carrier density decreased in the passive film, which restrains the passive film electrochemical reaction and improves the passive film stability. Therefore, the nanocrystallized bulk 304ss was more protective against chloride ion attacking in 0.05 mol/L H2SO4 ＋0.05 mol/L NaCl aqueous solution.