In order to reveal the influence of iron ion on the demulsification and dehydration of crude oil emulsion，the effect of iron ion on the stability of crude oil emulsion，the partition coefficient of iron ion between oil phase and water phase，and the type of iron ion in oil phase were investigated. The results showed that the dehydration ratio of the emulsion decreased during the demulsification with increasing iron ion content in the emulsion. In addition，the emulsion did not dehydrated when the iron ion content was 500 mg/L in an aqueous emulsion of 40%. The transition of iron ion from water phase to oil phase happened during the crude oil emulsification process. After 100，300，500 mg/L Fe²⁺ or Fe³⁺ solution were mixed with crude oil respectively，the partition coefficient of Fe²⁺ and Fe³⁺ in water phase was 0.2327，0.2013，0.2380 and 0.2658，0.1837，0.2515，respectively. After the crude oil was extracted by distilled water，acidulous water and acetonitrile，the corresponding average remove rate of Fe²⁺ and Fe³⁺ was 85.4%，96.5%，91.3% and 84.2%，94.8%，91.5%，respectively，which indicated that the iron ion mainly formed oil-soluble petroleum acid salt in crude oil. When the concentration of Fe²⁺ increased from 0 to 500 mg/L，the conductivity of emulsion increased from 0.008 to 0.025 μm/cm. The iron ion increased the stability and conductivity of crude oil emulsion，which made the demulsification become difficult and the time of peak current was extended during electric dehydration process. The emulsion containing 10% water led to short circuit of electric dehydrator when the mass concentration of iron ion was 1000 mg/L.