Abstract: Weizhou Formation of the Paleogene in Weizhou oilfield is an important field of petroleum exploration in Weixi’nan Depression, Beibu Gulf Basin, South China Sea. In order to implement the characteristics and influencing factors of high-quality reservoir in the third member of Weizhou Formation, the well with comprehensive basic data in Weizhou oilfield was taken as the research object to comprehensively analyze the reservoir of the third member of Weizhou Formation in Weizhou oilfield through core observation, thin section identification, mercury injection and scanning electron microscopy. The results show that the reservoir lithology of the third member of Weizhou Formation in Weizhou oilfield is dominated by feldspathic lithic sandstone. The physical properties are mainly medium-high porosity and medium permeability, and the reservoir space types are mainly intergranular pores, intergranular dissolved pores and intragranular dissolved pores. The third member of Weizhou Formation is dominated by braided river delta deposits, and the sedimentary facies control the reservoir distribution and the development of sand bodies. The characteristics of braided river delta under the background of transgressive systems tract determines that the third member of Weizhou Formation has the unstable sand-rich characteristics. The third member of Weizhou Formation is in an acidic dissolution diagenetic environment with weak compaction, and the secondary pores are developed. The secondary enlargement of quartz enhances the compaction resistance of particles. The research results are of guiding significance for determining the influencing factors of reservoirs in Weizhou oilfield.