Abstract: The reservoirs of Qingshankou Formation are from middle to thin in thickness and have the characteristics of tight, middle porosity, low permeability, complex pore structure, small trap scope, poor oil-water differentiation and complex relationship between oil and water. The existence of oil-water layers with the relatively low resistivity, water layers with relatively high resistivity, oil layers with normal resistivity and water layers with normal resistivity makes it difficult to identify oil and water layers due to their similitude log responses. The analysis results of the relationship between log responses and influencing factors, such as lithology, granularity, porosity, pore structures, indicated that the complex log responses were resulted from the combined factors such as lithology, granularity, porosity, pore structure, formation water salinity. On the basis of general analysis, the crossplot drawn by using a combined parameter and resistivity can be used to discriminate oil and water layers.