The clastic source for the deep water slope in the northern South China Sea are characterized by diversity, complexity and variability since 3Ma. The possible source area of the Miocene Zhujiang Formation in the Baiyun Sag, Pearl River Mouth Basin was studied by using petrological analysis of sandstones and heterologous biological limestones and rare earth elements of mudstones. It was shown that the fragments of the Zhujiang Formation sandstones were mainly consisted of metamorphic rock debris and volcanic rock debris, with many plutonic rock debris. Under cathode rays, the quartz were blue and purple brown, and the feldspars were bright blue. Heterologous bioclastic limestones were slope calcarenaceous debris flow deposits, and might come from the Miocene carbonate platforms in the Shenhu Shoal uplift. The average ΣREE of the mudstones is close to that of Mesozoic intermediate—felsic volcanic rocks in the Yanshanian fold belt, δEu had obviously negative anomaly, the distribution model of LREE enrichment and HREE loss was consistent with the upper crust and the acid volcanic rocks and granites in the Yanshanian fold belt. In the latest Oligocene, the South China Sea movement made the second sea floor spreading of the South China Sea basin and the jumping of the shelf break from the south side of the sag to the north in the Baiyun Sag. This tectonic event occurred in the adjacent basins around the Qinghai—Xizang(Tibetan) Plateau and also occurred in the eastern China basins, reflecting the occurrence of the Qinghai—Xizang(Tibet) Plateau uplift event, which made the provenance during the Zhujiang Period expand westward. Although active traction currents existed since the Zhujiang Period, the provenance was still the intermediate—felsic volcanic rocks and granites in the Yanshanian Fold Belt and ancient sedimentary—metamorphic rocks in the South China inlands, which were carried by the ancient Pearl River.