Abstract: In order to clarify the lithology, formation age, and tectonic attributes of buried-hill in the northern steep slope zone of Haizhong Sag, Beibuwan Basin, this study comprehensively utilized data from drilling cores, well logging, seismic and zircon U-Pb data to conduct petrographic analysis and age determination. Obvious metamorphism can be observed in the basement buried-hill core of Well X, and the lithology is comprehensively identified as low-grade metamorphic quartz sandstone. Seismic profiles reveal that the amplitude of the buried-hill in the study area is characterized by weak amplitude, poor continuity and clear macroscopic stratification overall. Well logs show low natural gamma ray values and high resistivity values. Zircon U-Pb dating results indicate that the youngest zircon ages range from 484 Ma to 429 Ma with a peak at 441 Ma.The findings demonstrate the presence of a Caledonian low-grade metamorphosed basement in Haizhong Sag. Trace element characteristics of the detrital zircons suggested that they were formed in a continental magmatic arc or orogenic environment, representing products of the Caledonian tectonic-thermal event. This low-grade metamorphic basement is comparable to Sinian-Lower Paleozoic low-grade metamorphic rocks of South China Plate, representing the offshore extension of the Caledonian fold belt. This study provides new age and lithological evidence for the tectonic evolution research and is expected to open up a new prospect for oil and gas exploration in the area.