As preferential flow channels in the reservoir during water-flooding, the dominant flow units are generally occurred at various scale and extents, ranging from um to hundreds of meters, and they are commonly attributed to the heterogeneity of pore systems and reservoir quality. The dominant flow units were found to be extensively developed in J oilfield, which lead to the rapid increase of water cut and the decline of oil production in oil wells. Therefore, it is of great importance to clarify the genesis and distribution of dominant flow units at various scales for the efficient development of water flooding oilfields. Since the weak correlation between flow capacity and primary permeability of flow units makes it difficult to identify dominant flow units. The parameters of water intake intensity ratio and relative water intake volume were served here to recognize dominant flow units. The linear discriminant analysis was used to construct the projection function that can best distinguish primary dominant flow units. Taking the contribution as the input weight of well logs, the difference of logging response of various flow units was determined by supervised self-organizing map, and the composition and distribution of dominant flow units in sand bodies are quantitatively characterized. The distribution of flow units is dominantly affected by carbonate cementation, and the organic acid in the oil have obviously inhibited the mes-genetic carbonate cementation, resulting in the favorable flow units mainly distributed in the high-position oil layers.