Abstract: The integrated analysis of geological settings, lithological sequences, paleontology, image well logging, seismic, etc. reveals that the sedimentary facies evolution after the faulting stage was a history of marine transgression in the North of Zhu III Depression, the Pearl River Mouth Basin. From the Zhuhai Formation to the Member 2 of the Zhujiang Formation, there are tidal flat, coastal plain and small delta facies; in the Member 1 of the Zhujiang Formation there are offshore and shelf sea facies; in the Hanjiang Formation there are shelf sea and large delta facies; and from the Yuehai Formation upto the Quaternary there are offshore and shelf sea facies. Three reservoir-seal assemblages have been recognized in the area, including: 1) the sandstone reservoir of the Zhuhai Formation and the Member 2 of the Zhujiang Formation coupled with the claystone seal bed of the lower part of the Member 1 of the Zhujiang Formation; 2) the standstone reservoir of the middle and lower part plus the claystone seal bed of the upper part in the Member 1 of the Zhujiang Formation; 3) the standstone reservoir in the lower part and the claystone seal bed in the middle part of the Hanjiang Formation. So far, oil has been discovered in the three assemblages.