Abstract: The research accuracy of sedimentary microfacies in the lower section of Huagang Formation and deeper strata in the southern Central Anticline Belt of Xihu Sag is limited, due to issues such as insufficient drilling depth and the quality of seismic data in the early stage. In recent years, based on newly obtained drilling and newly processed high-resolution seismic data, focusing on the the structural flanks, the research accuracy has been refined to the sublayer level under the framework of the sand formation. Taking Structure C as an example, the distribution and evolution of the sedimentary microfacies of H7 Sand Formation in the lower part of Huagang Formation are comprehensively interpreted. The study shows that distributary channels and interdistributary bays are developed in H7 Sand Formation in the study area. H7 Sand Formation is divided into three sublayers from bottom to top: H7c, H7b, and H7a. Vertically, the water body first deepened and then became shallower. The sand bodies of H7c and H7a are thicker and developed continuously in the plane. H7b is dominated by interdistributary bays. The flank of the C anticline has exploration potential for structural-lithologic composite traps, and the area around wells C3-C4-C5 is the overlapping part of the main distributary channel bodies across three depositional stages, which is the favorable facies belt. This study deepens the understanding of the deep stratigraphic sedimentary system in the southern Central Anticline Belt, and lays a foundation for further exploring the potential of structural-lithologic composite traps.