The electronic properties of passive films formed on G3 and G30 alloys in bicarbonate/carbonate buffer solution were comparatively studied by electrochemical impedance spectra(EIS) and Mott-Schottky analysis, the chemical composition of the passive film formed on G3 alloy was detected by X-ray photoelectron spectroscopy (XPS). The results show that passive film on G3 alloy had better protection than that on G30 alloy. The transfer resistance, film resistance and diffusion resistance of the passive films on both alloys increased with increasing formation potential, prolonging formation time, increasing pH value, decreasing formation temperature, and decreasing chloride and sulphide ions concentration. Mott-Schottky plot reveals that the passive films on the two alloys show a p-n semi-conductive character. XPS analysis indicates that the passive film on G3 alloy was composed of an inner Cr oxide and an outer Fe, Mo/Ni oxides. The electronic properties of passive films formed on G3 and G30 alloys in bicarbonate / carbonate buffer solution were comparatively studied by electrochemical impedance spectra (EIS) and Mott-Schottky analysis, the chemical composition of the passive film formed on G3 alloy was detected by X- The results show that passive film on G3 alloy had better protection than that on G30 alloy. The transfer resistance, film resistance and diffusion resistance of the passive films on both alloys increased with increasing formation potential, prolonging formation time , increasing pH value, decreasing formation temperature, and decreasing chloride and sulphide ions concentration. Mott-Schottky plot reveals that the passive films on the two alloys show a pn semi-conductive character. XPS analysis indicates that the passive film on G3 alloy was composed of an inner Cr oxide and an outer Fe, Mo / Ni oxides.