During the deposition of the Miocene Zhujiang Formation, the HZ Sag in the Pearl River Mouth Basin, South China Sea, was a stably deposited shelf setting. A large-scale paleo-Pearl River water system was developed in the western part of the study area and provided abundant terrestrial clastic deposits for the large-scale Pearl River Delta. A case study on sequence PSQ6 has been carried out in this paper. Depositional slope breaks were mainly developed during the ending time of the depositional period of highstand systems tract delta of underlying sequence. A regional “ditch-trough” system was formed along the area between depositional slope break and carbonate buildup in the east of prodeltaic subfacies. Thus a favorable source-reservoir-caprock assemblage is formed and stratigraphic-lithologic hydrocarbon accumulations usually occur in these areas.