The flowing unit is very important in the study of reservoir heterogeneity and the remaining oil distribution. In the current research methods for flow units, the seepage barrier distribution between the flow units is not well accounted for, too much emphasis is paid on the flow units in the vertical stratification, and the evaluation parameters are not adequate. To solve these problems, this paper considers the upper part of Guantao group strata of 12 and 20 well zones in Southern District of Chengdao oilfield. Combining logging, geological, and development data and other information, several parameters that would reflect the seepage features of the reservoirs are selected such as porosity, permeability, median grain size, clay content, sand body thickness, net/gross ratio, in an analytical hierarchy process, based on the analysis of sedimentary facies and the identification of seepage barriers, the flow units are studied by the cluster and discrimination method. The flow units in this area are divided into four kinds: E, G, M and P, and the formulas for these four kinds of flow units are derived. Compared with the production data, it is found that the distribution of major reservoirs and E-type flow units are in good agreement, showing that the study of flow units can provide a feasible means for the analysis of the heterogeneity and the distribution of remaining oil.