Abstract: In order to explore the diagenesis and development pattern of high-quality reservoirs of the Weizhou Formation in the Weixinan Depression of Beibu Gulf Basin, South China Sea, taking the third section of the Weizhou Formation in the Weizhou X Oilfield as an example, the types and mechanisms of diagenesis, the sequence of diagenesis evolution, and the division of diagenetic facies were analyzed in depth through techniques such as thin section microscopy identification, scanning electron microscopy, cathodoluminescence, and numerical simulation of diagenesis. The main controlling factors and selection of high-quality reservoirs were also carried out. The results show that the compaction effect of the reservoir in the third section of the study area is moderate, mainly in point line or line contact; The cementation process is mainly composed of different types of clay minerals, and is generally in the favorable stage of A₁²-A₂¹ micro stage of diagenesis; The research area has experienced acidic and alkaline dissolution, with typical kaolinite and chlorite acid alkaline dissolution products being the most prominent; The sedimentary diagenetic facies of distributary channel A₁¹ and distributary channel A₁² are the development facies zones of high-quality reservoirs in the study area.