Abstract: The interlayer development mode in the reservoir has an important impact on the degree of the reserve production level and the distribution of remaining oil and gas. A thorough investigation on the core, logging, test, and analysis was conducted for the H6 Reservoir of B Oilfield in the East China Sea to explain the complexity and the discrepancy between dynamic and static reserves and the low recovery efficiency. Through testing and analysis, the types, characteristics, and origins of interlayers were clarified, for which the logging identification standards of different types of interlayers in the study area were established and the spatial development mode of interlayers is described. Results reveal that interlayers in H6 Reservoir are mostly lithological (argillaceous layer) type, and their genesis is mainly regulated by high-frequency cycles. Other less distributed interlayers are cause by physical property discrepancy and formed during sedimentation at the bottom of the river bed. The occurrence of interlayers in the H6 Reservoir was seen in two types: inter-sandbody and intra-sandbody. The inter-sandbody interlayers have good continuity locally and distributed widely, playing a good role in obstructing the local fluid movement. However, the intra-sandbody interlayers are thin and sporadically scattered, thus have a limited blocking ability. This study offered a basis for future oilfield exploration in the H6 Reservoir.