Abstract: The influence of chloride ions (Cl^-) on the corrosion resistance of X80 pipeline steel in 0.5 mol·L^-1 NaHCO₃ solution was discussed by potentiodynamic polarization technique, and the corrosion mechanism was investigated by capacitance The results show that Cl^- enhances the occurrence of pitting corrosion of X80 pipeline steel in 0.8mol·L^-1 NaHCO₃, and the density and size of corrosion pits increase with increasing Cl^- concentration. Mott-Schottky results indicated that the value of donor density of the passive film increases with increasing Cl^- concentration, which enhances the potential sites of film local breakdown and corrosion initiation. It is concluded that the addition of Cl^- decreases the corrosion resistance of X80 pipeline steel in 0.5 mol·L^-1 NaHCO₃ solution.