Abstract: In view of the heterogeneity and various types of reservoirs in Shengli oilfield(fluvial positive rhythm de-posit,delta deposit and complex fault block reservoirs),mechanism study,pilot and field application of unstable waterflooding were performed.Unstable waterflooding was verified to be able to enlarge sweep efficiency and en-hance the ultimate oil recovery.This technique has the outstanding advantages of small investment needed,rapid response speed and prominent increase of production and is an effective technological measure to deepen secondary recovery and improve development effects of waterflooding reservoirs.