The effect of Ca^2＋ on CO2 corrosion to X65 pipeline steel was investigated in the simulated stratum water of an oil field containing different concentrations of Ca^2＋. It is found that Ca^2＋ can enhance the corrosion rate, especially in the Ca^2＋ concentration from 256 to 512 mg/L, which can be attributed to the growing grain size and loosing structure of corrosion scales with increasing Ca^2＋ concentration. X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） investigations reveal that a complex carbonate （Fe, Ca）CO3 forms at high Ca^2＋ concentration due to the gradual replacement of Fe^2＋ in FeCO3 by Ca^2＋.
