Abstract: Bohai L oilfield is characterized by big thickness of single layer and no obvious interlayers. Starting from the influencing factors such as reservoir heterogeneity, gravity impact, interlayer distribution, corresponding rate and intensity of injection-production, in combination with theoretical research and comprehensive analysis of dynamic and static data, the detailed study on water flooded and residual oil distribution regularity of thick oil layers has been carried out and reasonable understanding has been obtained, not only providing powerful technical support and guidance for comprehensive adjustment and tapping measures of the oilfield, but providing the experience for reasonable and effective development of the same kind oilfield.