We analyzed the sequence stratigraphy and biostratigraphy (based on the abundance of foramini- fers and calcareous nannofossils) of 27 drill cores in the Yinggehai-Qiongdongnan Basin. Twenty third-order sequences were recognized in Oligocene TB1. 1 to Quaternary TB3.9 strata. Based on the abundance and diversity of microfossils, assemblage characteristics, and estimated water depths, paleoenvironments were reconstructed for reservoir sandstones in $29-28 under the "fault No. 1" zone. The study establishes a sequence stratigraphic framework and a sedimentary facies model for the Yinggehai-Qiongdongnan Basin.