Abstract: The conventional way to study minor-layer residual oil is to calculate the present saturability of residual oil according to the static and dynamic data and allocate it to the minor layers so as to determin the potential residual oil regions in the whole oil area macroscopically. In this paper, the principle of balance of profit and loss is applied to analyse the low-efficient oil wells with low residual oil saturability microscopically from the technical economic angle, and the range and horizon of distribution for residual oil is pointed out further. This also provides basis for the decision of oil field development.