Abstract: The Mesozoic granite buried-hills in the Panyu 4 Sag, Zhu I Depression, Pearl River Mouth Basin are rich in hydrocarbon resources and a potential area for oil and gas exploration in the buried hills in the eastern South China Sea. To further understand the development mechanism of granite buried hill reservoirs in the area, the reservoir types, distribution characteristics, and main controlling factors were identified through thin section, logging, and seismic-scale pore and fracture identification. The following achievements and understandings were obtained: (1) The middle and low level buried hills in the sag develop mainly weathered fracture-type reservoirs, while the high level buried hills in the peripheral uplift zone of the sag developed mainly weathered sandstone and gravel+weathered fracture typed reservoirs. (2) The storage space of the buried-hill reservoir is composed of mainly fractures, which are jointly controlled by tectonic, diagenetic, and lithological processes. Among them, the pre-existing fault activities and magmatic reworking during the Yanshanian-Himalayan periods laid the foundation for the development of the reservoir fracture systems, promoted the development of tracking tension fractures, and increased fracture apertures, followed by multi-stage fluid alteration involving meteoric freshwater, deep hydrothermal fluids, and organic acids in later stages. (3) The study area features strong hydrocarbon charging dynamics. Future exploration should be prioritized in high-quality reservoirs located at the intersections of highly active faults in the advantageous hydrocarbon supply mode of the buried hill zone. The above achievements have certain guiding and reference significance for further exploration, evaluation, and geological research of the ancient buried hill hydrocarbon reservoirs in the area.