Abstract: In view of the development characteristics of inhomogeneous thick oil reservoirs at ultra -high water-cut stage in Shuanghe oilfield and starting withrevealing the intrastratal structure of thick oil reservoirs,this paper studics the genesis and distribution patterns of residual oil, residual oil enrichment position, types and control factors of its formation at ultra - high water -cutstage in inhomogeneous thick oil reservoirs through intraformational 3- D quantitativc fine description, finenumerical modeling and evaluation.