Abstract: An overall investigation on the pressure drop characteristics of oil-water emulsions for surface driven screw pump system is perfonned.The phenomenon of phase inversion between oil-in-water(O/W) emulsion and water-in-oil(W/O) emulsion is experimentally studied by measuring frictional pressure drop.The effects of the rotation of sucker rod on axial frictional pressure gradients of O/W and W/O emulsions are analyzed.The experimental and analytical results show that the water volume fraction at which phase inversion occurs is about 0.41-0.43.The effect of rotation on frictional pressure drop for W/O emulsion seems to be greater than that for O/W emulsion.The correlations on frictional resistance in different flow patterns for power law fluid flow through the annulus are obtained by means of experimental data processing.These research results possess a certain reference value to the design and application of the screw pump.