The aged oil is a type of oil-water solid mixture with high emulsion stability formed at the the oil-water transition layer in crude oil tanks after long-term exposure to oxygen aging. It is difficult to treat using the conventional demulsification and dehydration treatment method. In this paper，through testing the oil-water interfacial tension and interfacial film strength of the aged oil in Hongqian oilfield，the influence of solid particles，polymers，inorganic salt ions and oxygen exposure time on the emulsification stability of the aged oil system was analyzed. At the same time，the demulsifier dehydration experiments were carried out on the aged oil，and finally the optimal demulsifier formula and process parameters were obtained. The results indicated that when the dosage of solid particles and polymers was increased and the exposure time was prolonged，the emulsion stability of the aged oil was enhanced，leading to increased difficulty in demulsification treatment of the aged oil. Inorganic salt could reduce the interfacial film strength of the aged oil，which was conducive to the demulsification of the aged oil. A demulsifier composed of polyethylene glycol octylphenyl ether（X-100）and sodium dodecylbenzenesulfonate（ABS）in mass ratio of 3∶1，could achieve good dehydration effect with dehydration rate of 100% and clear water quality，when the dosage was 2%，the demulsification temperature was 60—65 ℃，and an effective settling time was more than 30 minutes. The formulation and process parameters formed by the experimental research in this article provide technical guidance for the treatment of the aged oil in Hongqian oilfield. At the same time，the emulsification characteristics of the aged oil in the oilfield and the experimental rules for selecting demulsifiers obtained from the experiment can provide reference for the treatment of the aged oil in other oilfields.