Abstract: Shallow-water delta deposits are developed in the Oligocene Huagang Formation in the Xihu Sag of the East China Sea Basin. However, due to the rapid lateral variation in sedimentary facies in shallow-water deltas and the scarcity of offshore drillings and cores, understanding of these deltas is limited in local areas, and in-depth research into the distribution of sand bodies in the sag is difficult to perform. Based on available drilling data, regionally integrated seismic data, and core samples from the study area, we delineated the sedimentary facies zones and the sand bodies of shallow-water deltas in area of approximately 3,000 km² in the central part of the sag, by detailed analysis of sedimentary microfacies and sand body development in key areas. Results show that vertically, sedimentary microfacies changed rapidly within individual sand units, while horizontally, mixed zones were formed by microfacies overlapping from different periods. During flood season, the paleo-shoreline was located near slope area, whereas during dry season, the paleo-shoreline advanced significantly toward the center of the sag, forming extensive delta-front sand bodies. Between the paleo-shorelines of flood season and dry season, a mixed zone of delta plain and delta front facies formed. From the sag slope to the sag center, numerous delta plain channel sand bodies, delta front channel sand bodies, and beach-bar sand bodies were developed, resulting in a "basin-wide sandbodides" pattern in the central part of the sag. These sand bodies, superimposed on anticlinal traps or structural ridges, formed numerous composite lithologic-structural traps. Drillings in some of these sand bodies confirmed that they are hydrocarbon-rich and potential of the discovery of several medium to large gas fields, thereby, thereby opening up the hydrocarbon exploration prospects in this region.