Traditional oil-water separation hydrocyclone mainly uses different centrifugal force between oil and water to achieve rapid separation. However, with gradual expansion of oilfield polymer flooding, ASP (alkali-surfactant-polymer) flooding, and other oil displacement technologies, viscosity of produced fluid is increasing, and emulsification is serious, then the efficiency of separation is greatly affected. Therefore, it is intended to add another field on the basis of centrifugal force field to realize oil-water separation under a stronger coupling field. Subsequently, concept of magnetic field is introduced into hydrocyclone. High efficient separation of hydrocyclone under the coupling of a centrifugal force field and magnetic field could be achieved, and a kind of magnetic hydrocyclone (MHC) is designed. Structure and separation principle of the MHC are introduced. During the separation process, magnetic particles are subjected to centrifugal force and magnetic force simultaneously, so they could "carry" or "push" part of the oil droplets towards the center of the hydrocyclone through contact and collision between magnetic particles and oil droplets, and ultimately achieve more efficient separation of oil and water. Firstly, the PIV (Particle Image Velocimetry) experiment was carried out. Then numerical simulation of coupling between a centrifugal force field and a magnetic field was conducted on the basis of theoretical calculation. Simulation results indicates that the magnetic force on particles for hydrocyclone having an optimum separation performance is 7.5 x 10(-8) N. Initial efficiency was 74.9%, and the efficiency was increased to 98.1% after applying a magnetic field. Through PIV test and numerical simulation analysis, it is found that the MHC has an obvious improvement on oil-water separation effect. It also provides a new idea for separation methods and structure designs of hydrocyclones.