Dominant flow path tends to be formed in the low permeability reservoir after long term waterflooding in mediumhigh water cut period，which results in invalid water circulation and severe impact on the water flooding result. Low-porosity and medium-low permeability reservoirs in the Sanjianfang Formation of Wenxi1 block in Wenmi oilfield were taken as examples. Controlling factors of the formation of the dominant flow path were analyzed according to lithology，deposition and microscopic characteristics. An approach to identify the dominant flow path was proposed by use of dynamic and static data and standards suitable for the study area were given. A comprehensive evaluation index model was built up through optimizing dynamic and static parameters. The results suggest that the formation of the dominant flow path in the Sanjianfang Formation of Wenxi1 block is controlled by the lithology，sedimentary facies and microscopic characteristics. The static characteristics are concluded as coarse lithology，good physical property and deposited on the main stream line of underwater distributary channel. The dynamic characteristics include the difference of water injection profile，the sudden rise of water cut in production wells and the rapid flow and breakthrough of tracer material with thin layer. The judging criteria are as follows：permeability is larger than or equal to 40×10-3 μm2；permeability ratio is larger than or equal to 20；pore and pore throat radius is larger than or equal to 3.6 μm；monthly increase of water cut is larger than or equal to 30%；water absorption in single layer is larger than or equal to 50%.