Abstract: The influence of iron naphthenate on the stability of oil-water emulsion and the iron removal mechanism of aging crude oil was studied. Results showed that with the increase of iron naphthenate in emulsion, the size of water droplets and water removal rate decreased, oil content in water and the negative value of zeta potential increased, indicating that the stability of emulsion increased. The water and iron removal rates of crude emulsion with BSE-238 demulsifier could be enhanced by adding compound complexing agent of polyaspartic acid and acetic acid (mixed with mass ratio of 1:1) containing 50 mg/L of HCl, NaCl and methanol respectively. The demulsification and deferrization mechanism was discussed by using polarized light microscopy and conductometric titration. It was found that both polyaspartic acid and BSE-238 demulsifier could promote the aggregation of water droplets and reduce the stability of emulsion. Polyaspartic acid could react with iron in crude emulsion and form an ionic water-soluble complex, which could be further removed with the proceeding of dehydration, resulting in the increase of aqueous solution electrical conductivity. The arranged simulation tests showed that the curve of changing in electrical conductivity was consistent with the suggested iron chelating mechanism.