Objective To investigate the influences of contents of chloride and sulfur ions on corrosion rates of 316L stainless steel and nickel-based alloy Monel in crude oil fractions and overhead aqueous phase of crude oil unit. Methods The corrosion rates of 316L stainless steel and Monel alloy in aqueous phase and oil phase containing different concentrations of chloride ions and sulfur ions were obtained by corrosion coupon experiment. SEM ( scanning electron microscope) was used to observe the surface microstructure of corroded 316L and Monel alloys. The influence of two kinds of ions on the corrosion of 316L stainless steel and Monel alloy was discussed. Results The corrosion rates of 316L stainless steel and Monel alloy in highly acidic desalted crude oil were 0. 0091 mm / a and 0. 0248 mm / a, respectively. And in weak acidic second fraction, the corrosion rates were 0. 0078 mm / a and 0. 0031 mm / a, respectively. In second fraction, after addition of 600 mg / L of chlorine ion and 30 mg / L of sodium sulfide, the corrosion rates of 316L stainless steel and Monel alloy were 0. 1755mm / a and 0. 1707 mm / a, respectively. Meanwhile, in the desalted crude oil with the same concentrations of chloride ions and sulfide ions, the corrosion rate of 316L stainless steel was 0. 0545 mm / a and that of Monel alloy was 0. 1281 mm / a. Conclusion The results indicated that the naphthenic acid corrosion was the dominant factor when there was little chloride in oil phase and the chloride corrosion turned into the major factor if the content of chloride in oil was at high levels. The corrosion rates of the 316L stainless and Monel alloy raised with the increase of chloride ion concentration in oil phase. Furthermore, the existence of sulfur ions could accelerate corrosion in oil phase. In contrast, chloride and sulfur ions did not have apparent impact on the corrosion of Monel alloy in aqueous phase.