Abstract: Chang 61 reservoir of Fanchuan area generally belonged to low resistivity reservoir,which made it difficult in oil layers' identification.By contrasting laboratory tests and production data,combined with geological characteristics of Chang 61 reservoir,by means of the methods of cross-plot and natural potential overlaps,the genetic analysis of low resistivity was carried out.The results indicated the complicated pore structure of Chang 61 led to higher irreducible water saturation and higher formation water salinity,and the increased conductivity of clay minerals was the main reason of low resistivity.It was concluded the methods of cross-plot method and natural potential overlaps could effectively identify the low resistivity reservoir.