Quantitative analysis of the source- to- sink system is the leading edge of the field of sedimentology, and is of great significance for accurate reconstruction of source- to- sink process and prediction of hydrocarbon reservoirs. Methods:We use the heavy mineral assemblages and zircon U- Pb ages to trace the provenance of the Huizhou- 27 transfer zone in the Huizhou Sag, Pearl River Mouth Basin, and quantitatively reconstruct the sediment contribution of potential source areas. In addition, we reveal the source- to- sink process and discuss the control of source- to- sink system on the hydrocarbon reservoir. Results:The results show that the heavy mineral assemblages of the middle Eocene Wenchnag Formation are complex with low ZTR values（the ZTR index is the percentage of detrital zircon, tourmaline and rutile in the transparent heavy mineral detritus of a clastic rock）, while the heavy mineral assemblages of the upper Eocene Enping Formation are relatively simple with high ZTR values. This study further confirms that the Wenchang Formation to the Enping Formation were mainly fed by intrabasinal Mesozoic magmatic basement and extrabasinal Pearl River system. For the Wenchang Formation, ca. 98% sediments were derived from the intrabasinal Mesozoic magmatic basement; for the lower Enping Formation, ca. 58.4% sediments were derived from the northeastern tributaries of the Pearl River, while ca. 36. 5% sediments were derived from the intrabasinal Mesozoic magmatic basement; for the upper Enping Formation, ca. 73. 7% sediments originated from the northeastern tributaries of the Pearl River, while ca. 22. 2% sediments originated from the intrabasinal Mesozoic magmatic basement. Conclusions: We infer that the modern Pearl River system, including the northeastern and western tributaries, was not yet formed during the depositing of the Enping Formation, but the northeastern tributaries (i.e., the paleo- Pearl River) had developed independently. Rather than a simple provenance transition from intrabasinal to extrabasinal, the paleo- Pearl River transported abundant sediments from the Cathaysia Block into the Huizhou Sag, resulting in the transition of the source- to- sink system from “the Wenchang Formation with intrabasinal provenance” to “the Enping Formation with mixed provenance”. This transition of source- to- sink system changes the rock composition of reservoir in the Enping Formation, which improves the reservoir physical properties but enhances the reservoir heterogeneity. This study presents a quantitative analysis of the transition of the source- to- sink system in the Paleogene Huizhou Sag, and provides insights into the quantitative source- to- sink process and its applications in continental rift basins.