Abstract: Downhole oil-water separation and single-well injection and production technology is an effective method to realize the economic development of high water cut oilfields. After decades of research and development, several downhole oil-water separation ways have been formed, such as cyclone separation and gravity settlement. Meanwhile, the supporting centrifugal pump, screw pump, sucker rod pump as well as other dynamic systems and packer systems are developed. But many problems still exist in technical stability and reliability. The application scope is affected by medium parameters, process characteristics, reservoir parameters and etc., thus restricting the technical promotion and application. With the advancement of technology, the downhole oil-water separation and single-well injection and production technology is developing to achieve high efficiency, stable operation, small scale, low cost and intellectualization. The axial diversion inlet hydrocyclone has been developed to fit the 139.7 mm(5-1/2 inch) cased well. Research and application is carried out on the cubic curve and endocone hydrocyclones, multistage-series cyclones and other separators, so as to improve the effect of oil and water separation. Modular hydrocyclone technology has been developed to cut down the manufacture cost. The optimized supportive technology for single-well injection and production system has been created to enhance the level of trouble shooting and remote monitoring. The technical adaptability has been improved, and reservoir adjustment has been achieved by block application using engineering technology, so as to stabilize oil production, control water production, save energy and reduce consumption. It is a new "downhole factory" development mode, heralding the development of the fourth generation oil recovery technology.