The source areas changed obviously during Oligocene/Miocene in the northern w:st="on">South China Sea. With the point-counting method of thin sections of Miocene Zhujiang Formation and Oligocene Zhuhai Formation in Baiyun Sag, w:st="on">w:st="on">Pearl River w:st="on">Mouth w:st="on">Basin, the characteristics of detrital components were studied in detail. The results show that: the lithic fragments in Zhuhai Formation were dominated by plutonic magmatic fragments, and there were also many feldspar and sedimentary lithic fragments, in agreement with the fact that the source was mainly from Mesozoic granite rock in the South China; in contrast, the lithic fragments were dominated by metamorphic fragments in Zhujiang Formation, and there were some magmatic fragments, sedimentary fragments and more feldspar, indicating more supply of the sources in Zhujiang Formation.