Abstract: Aiming at the problem that the origin of coarse clastic deposits in the lower part of Huagang Formation in north-central part of the central anticlinal belt of Xihu Sag is unclear, on the basis of drilling data, through the combination of sequence stratigraphy and sedimentology, the sedimentary system evolution process and facies migration characteristics of lower Huagang Formation are explained dynamically. Under the current three-level sequence framework, lower Huagang Formation is further refined to the system tract level by combining well-log and seismic data. Under the elaborate stratigraphic framework, the sedimentary system and distribution characteristics of Huagang Formation are identified by source analysis, well logging characteristics and core characteristics. The results show that the northwest provenance supply is strong during the Huagang Formation period. The braided river delta depositional system in the long axis direction of northeast is mainly developed in the study area. The coarse debris mainly comes from braided channel deposits and branched channel deposits of the delta plain in the lower system tract. This study deepens the understanding of coarse clastic bodies in the north-central part of the central anticlinal belt and provides a basis for the study of reservoir formation conditions in the central anticlinal belt.