Abstract: The Mesozoic buried hill in Qiongdongnan basin is an important window to understand the tectonic evolution of the western continental margin of the South China Sea. This paper presents systematic petrographic, geochronological and geochemical studies on the granite buried hills of Lingnan low uplift and Songnan low uplift in the Qiongdongnan basin, aiming to reveal their petrogenesis and tectonic environment. The results showed that the buried hill in Lingnan low uplift (L321−a and L281−a) is mainly comprised by monzogranite, while those in Songnan low uplift (Y83−a and Y83−b) are mainly composed of granodiorite and monzogranite. Zircon U−Pb dating show that the studied granitoids in Lingnan low uplift were formed at 249 Ma and 233 Ma, while those in Songnan low uplift were formed in 222~219 Ma. Petrogeochemical study shows that the A/CNK values of the granitoids in Lingnan low uplift range from 1.04 to 1.15. They are generally enriched in large ion lithophile elements such as Rb, Th and U, and depleted in high field strength elements such as Ta, Nb and Ti, belonging to weakly peraluminous, high potassium calc−alkali I−type granite. The granitoids in Songnan low uplift have high contents of alkali (K₂O+Na₂O=6.74%~8.41%), but low contents of aluminum（Al₂O₃ = 12.52%~13.70%）with high ratios of Rb/Sr (2.03~9.20) and 10000 Ga/Al (>6). They are enriched in light rare earth elements with weak negative Eu anomalies, resembling typical A−type granite. Petrogenesis study shows that the Triassic granitoids in the Qiongdongnan basin are derived by partial melting of sedimentary rocks, followed by different degrees of crust−mantle mixing and fractional crystallization. This study reveals that the Early Triassic granitoids in the Qiongdongnan basin were formed in a convergence and syn−collisional setting during the Paleo−Tethyan subduction, while the Late Triassic granitoids were formed in a post−collision extensional setting. The large−scale Early Triassic granitoids in the Qiongdongnan basin not only contains a high proportion of felsic brittle minerals, but also underwent multiple stages of tectonic transformation during the subduction−collision and post−collisional extension, providing the material basis and dynamics conditions for forming fractured buried hill reservoirs. Thus, the Early Triassic granitoids in the Qiongdongnan basin are an important object for buried hill−related oil and gas exploration in the South China Sea.