The Paleogene Fushan Sag in Beibu Bay Basin is characterized by small area, multiple sources as well as complex and variable depositional systems, and the source- to- sink correlation and coupling are poorly understood. Methods: By multiple methods of seismic foreset reflection, zircon U- Pb dating, heavy mineral assemblage and distribution of sandstone percentage, the provenance of the upper submember, First Member, Liushagang Formation, was investigated to determine the source- to- sink relationship, and then different source- to- sink coupling models of the Late Eocene Fushan Sag were established to guide favorable reservoir prediction. Results:The results show that the seismic profiles from southern gentle slope, western steep slope and eastern steep slope zones exhibit obvious foreset reflection; similar to those from Hainan Island, the zircon U- Pb age spectra of Yong’an and Huachang areas are characterized by double peak ages; the heavy mineral assemblages of the Fushan Sag can be classified into four categories, i.e., Chaoyang area in the western steep slope zone, Jinfeng area in the eastern steep slope zone, Meitai and Yong’an areas in the west side of the southern gentle slope zone, and Huachang and Bailian areas in the east side; the high percentage values of sandstone can be seen along Meitai, Huachang and Bailian areas in the southern gentle slope zone, which can be extended to Yong’an area in the north, and the median percentage values of sandstone can be seen in Chaoyang area in the west and Jinfeng area in the east. Conclusions: Comprehensive analyses indicate that the Late Eocene Fushan Sag had three major sources, i.e., Hainan Island in the south, Lingao Uplift in the west and Yunlong Uplift in the east, of which the source of Hainan Island can be divided into east and west branches. The Late Eocene Fushan Sag is further divided into three secondary source- to- sink systems, including Hainan Island—southern gentle slope zone, Lingao Uplift— western steep slope zone and Yunlong Uplift—eastern steep slope zone. From the perspective of source- to- sink system, the underwater distributary channel in the source and sink system of Hainan Island—southern gentle slope zone is a favorable zone for high- quality reservoir development.