Abstract: The Qiongdongnan Basin constitutes a significant gas hydrate accumulation zone in the northern South China Sea. The environment and age of its hydrate reservoirs is crucial for understanding the formation and guiding exploration development. We analyzed the foraminiferal and calcareous nannofossil biostratigraphy of sediments from boreholes W07B, W08B, and W09 in the Songnan low uplift from the GMGS5 Expedition, and boreholes W01, W03, and W04 in the Lingnan low uplift from the GMGS6 Expedition. The formation time of the reservoir was precisely determined and the depositional environment investigated. Three foraminiferal biozones and two calcareous nannofossil biozones were identified, revealing the oldest strata as being Middle Pleistocene, approximately 0.75 Ma old. Hydrate reservoirs formed mainly since 440 ka B.P., exhibiting a high sedimentation rate from 25.67 to 45.44 cm/ka. The environment has been unstable since 440 kaB.P., with multiple disturbance by shallow-water allochthonous deposits. The hydrade deposits were characterized by the abundant occurrence of benthic foraminifera from nearshore and shallow marine environments, low CaCO₃ content, increased terrigenous material, and coarser sediment grain size. The high sedimentary rate of over 20 cm/ka and exogenic transport provided favorable storage space for hydrate formation, particularly for seepage-type hydrate development. Allochthonous deposition was the key controlling factor for hydrate accumulation in the study area.