Abstract: With the development and production of S oilfield, the plane and interlayer contradiction gradually reveal. In order to stabilize the production oilfield, slow oil production decline and enhance oil recovery, under the guidance of "water injection enough, water injection well", a lot of work to strengthen water flooding and optimize water flooding have been conducted in S oilfield, which enable the formation pressure in each block of the field to recover and rise to different extent and the interlayer contradiction be improved effectively. The study and application of water injection optimization in S oilfield has achieved good effects and economic benefits.