Pipeline integrity is maintained mainly by coating and cathodic protection (CP). The interaction between hydroxyl ions produced by CP-driven cathode reactions, such as water reduction, and carbon dioxide in soil generated by the decay of organic matter may develop high-pH of concentrated carbonate-bicarbonate electrolyte. The dominant anodic dissolution process of the corrosion of pipeline steel in the exposed environment could cause the degradation of the pipeline. In addition, aggressive ions, such as chloride ions, existed in soils would have an accelerating effect on the anodic process. The effect of 0.4 T magnetic field on the anodic process of X70 pipeline steel in sodium carbonate solution with and without chloride ions was studied using anodic polarization curve measurement, potentiodynamic scanning and potentiostatic polarization measurement. The anodic polarization curves of X70 pipeline steel in sodium carbonate solution show that the applied magnetic field increases the current density of oxygen evolution reaction at a high potential range, while has no significant effect on the anodic reaction at the passive range. In the sodium carbonate solution containing chloride ions, when the potentials for potentiostatic polarization are located in the passive range near the transition range of the potentiodynamic polarization curve; the potentiostatic polarization curves exhibit the characteristic of rapid active dissolution, and the applied magnetic field inhibits the anodic dissolution. When rapid anodic dissolution reaction and oxygen evolution reaction occur simultaneously at a high potential range, the effect of the magnetic field is not significant. The difference in anodic polarization current density obtained by potentiodynamic scanning polarization and potentiostatic polarization is due to the differences in electrode surface state and electrode reaction type caused by different polarization methods, leading to the alteration of the magnetic field effect.