Abstract: As offshore oil field is characterized by less test data, large well spacing,multi- layer producing and serious interference layer,the residual oil distribution,which is the basis of adjustment programs,becomes more complex.Take an example of heavy oil field in the sea,based on detailed geological studies and through time - lapse seismic,reservoir engineering,reservoir simulation and other methods,the in - depth study on residual oil distribution in vertical and horizontal direction was carried out.And therefore,the distribution law of heavy oil field with large well spacing and commingling production was obtained.Besides that,through sealed coring data analysis,the understanding on residual oil was further verified.The study shows that the method could also be applied in other oilfields with the same kind.