Abstract: With the continuing development of Bohai Oilfield, the increasing water cut in produced fluids has made oil stabilization, water control, and enhanced oil recovery (EOR) a critical issue in offshore oilfields. Downhole oil-water separation (DOWS) technology, which utilizes downhole hydrocyclones for downhole oil-water separation, is a promising solution that effectively reduces overall development costs. This paper conducts an in-depth study on the demulsification and oil-water separation processes of oil-water emulsions by using downhole cyclones, focusing on the influence of four key factors: separation time, centrifugal speed, operating temperature, and demulsifier concentration on the oil-water separation efficiency. The research results show that with the increase of separation time, the oil content in the aqueous phase first decreases rapidly and then tends to be stable. Increasing the centrifugal speed, temperature, and demulsifier concentration significantly reduces the oil content in the aqueous phase. However, when the demulsifier concentration exceeds 300 mg/L, the oil content in the aqueous phase increases instead. Additionally, the interaction between each factor and separation time does not show significance, indicating that their impact on oil content is mainly through independent effects. This study provides important theoretical foundation and practical guidance for optimizing downhole hydrocyclone operating parameters and enhance oil-water separation efficiency, offering significant application value for the efficient advancement of offshore oilfield development.