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For improving the corrosion resistance of 904L stainless steel under high Cl- concentration environment with different pH values condition，the corrosion behavior of 904L austenitic stainless steel in 100 g/L NaCl solution at different pH values was studied by cyclic polarization curves，electrochemical impedance spectroscopy，Olympus confocal microscopy，scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Results showed that the corrosion resistance of 904L stainless steel increased with the increase of pH value，EIS consisted of two capacitive reactance arcs，and the radius of capacitive reactance arc increased with the increase of pH value，and the capacitive reactances were all in the same order of magnitude.Meanwhile，lower pH value conditions could enhance the destructive effect of Cl- on the passive film.With the decrease of pH value，the range of passive region of the material decreased.When the pH＝2，slight pitting occurred on the surface of the material.