Abstract: Chang-6 reservoir of Yanchang formation in Huaqing area of Ordos basin is a typical clastic reservoir.By taking Chang 6_3 oil reservoir as an example,according to the basic theory and methods of flow unit,based on core analysis data and well logging data of 7 key wells,the flow indicators and reservoir quality index have been selected and calculated.In combination with permeability,porosity,reservoir quality index and standardization porosity index,the flow units of Chang 63 reservoir can be divided into Ⅰ,Ⅱ,Ⅲ and Ⅳ four categories.Study results have shown that the capacity and flow capacity of type- I is the best but with the least distribution.The flow units of type-Ⅱ and type-Ⅲ are more but with poorer reservoir and flow capacities,which is in line with low porosity and ultra-low permeability reservoirs.