The cyclone plays an important role in the downhole oil-water separator during artificial lift for high water cut oil well, the processes of oil-water separation is completing in the cyclone. The oil-water cyclone separator was designed based on the oil and water density contrast and the cyclone separation theory; the laboratory experiment of cyclone separator was carried out and the relationship of the cyclone oil cut of apex and split ratio, oil-water separation efficiency and the velocity , the pressure loss of the cyclone and the velocity were also studied. When the reinjectivity is within 70% of the produced volume, cyclone separator has good water-oil separation ability, split ratio increased with the increase of the vecolity, when the flow vecolity reached 0.25m/s, the split ratio over 30%. But with the increase of the velocity, the increased rate of the split ratio is reduced. The relationship of the flow rate and cyclone intrinsic pressure loss is nonlinear exponential curve.