Abstract: The Gudao oil field produces viscous oil from unconsolidated sand pays and has an oil-water viscosity ratio up to 50-300 or more. This paper describes, in three parts, the studies on the performance of water flooding for enhancement of production and the law of oil and water movement, and the way to improve its recovery during the middle stage of water cut. Firstly, the effect of viscosity and fhlid heterogeneity on oil and water movement is analysed. Secondly, the effect of combined injection-production adjustment on recovery during middle stage of water cut in the Gudao field is discussed, especially in respect to its southern part of Central Ⅱ. Lastly, measures for controlling the rate of water cut and increasing recovery during the middle and lower stages of water cut are reviewed, that involve expanding the area of sweep and applying selective injection on the basis of multizone production and pattcrn flooding.