Abstract: Using both geological and geophysical methods, this paper aims to study the evolutionary and depositional features of the Baiyun Sag, Pearl River Mouth Basin, the Northern South China Sea. The results show that during the period of Early-Middle Eocene, the Baiyun Sag was prevailed by a transition from alluvial fan to deep lake facies, with marine transgression sometimes in late Eocene. The sediments are mainly sourced from the Panyu Lower Uplift and the Shenhu Plateau. In Early Oligocene, the study area turned gradually to transitional and marine environment. Provenances in the north part of the sag were controlled by the Panyu Lower Uplift, while the sag was mainly filled with sediments from the western SCS through “Kontum- Ying-Qiong” Rivers. The Pearl River started exerting influence on the north part of the sag in Late Oligocene as it passed over the Panyu Lower Uplift, and the rest parts of the sag were controlled by double sources from both the “Kontum-Ying-Qiong” River and the Pearl River. Since Miocene, the water depth constantly increased due to the southward jumping of slope break and increase in basin subsidance, which resulted in the fully domination of ancient Pearl River sediment and the complete transformation of the southern part into deep water environment. The southern part of the sag since then has been influenced by the mixed sedimentation of turbidity current with terrigenous and oceanic sediments.