Interlayer characterization in sparse well area of offshore oilfield is a difficult problem in reservoir characterization. Taking the H3 sand group of X oilfield in Xihu sag, East China Sea Basin as an example. Based on the analysis of the genetic type of the interlayer, the identification standard of the electrical characteristics of the interlayer was established, and the spatial distribution of the interlayer was semi-quantitatively characterized by the method of geological and seismic coupling. The results show that the H3 sand group develops six interlayers: flood type, abandoned channel type, silt type, channel retention type, fine-grained sedimentary type and diagenesis type. According to the permeability of the interlayer, the flood type, the abandoned channel type and the silt fall are classified as the muddy interlayer, the channel retention type and the fine-grained sedimentary type are classified as the physical interlayer, and the genetic type is classified as the calcareous interlayer. The interlayer between H3a and H3b in H3 sand group is very developed, with large thickness, good continuity, stable distribution in the whole area and good sealing effect. the interlayer between H3b and H3c is unevenly developed, and the thickness is thin in the north of X10, west of X7-X8, X4-X5 area and the southwest of X1, resulting in weak connectivity between H3b and H3c sand bodies. The research results better characterize the distribution of interlayers in the H3 sand group, and provide a geological basis for remaining oil analysis. The method of geological and seismic coupling can effectively describe the interlayers in the thin well pattern area of offshore oilfield, which has a good reference for the fine characterization of reservoirs in similar areas.