Xishanyao Formation reservoir belongs to low oil saturation reservoir because of its low oil saturation and high water production rate. The coincidence rate with the employment of logging response including true resistivity is 67% because of the coexistence of low resistivity oil-water layers and high resistivity water layers. A fluid identification method was developed based on the cause analysis of low resistivity oil-water layers and high resistivity water layers, the definition of oil content index, and the cross-plot. Firstly, some factors affecting resistivity such as lithology, porosity, permeability, oil saturation were analyzed and it was found that the origin of coexistence of low resistivity oil-water layers and high resistivity water layers was the difference of low salinity drilling mud among the wells and intrusion. Secondly, R_t/R_mf was defined as oil content index to weaken the affection on resistivity from the salinity difference of drilling mud among the wells and intrusion based on the assumption that all the brine was mud filtrate within the detection range of true resistivity. Finally, the R_t/R_mf-density cross-plot was chosen as fluid identification cross-plot and 7 was calibrated as the lower limit of R_t/R_mf of oil-water layers by the results of oil testing. The results shows good application effect that oil-water layer in well Xiayan 18 and the water with oil layer in well Yan 1175 were identified matched the results of oil testing and the coincidence rate was increased from 67% to 92%.