Abstract: The distribution of lacustrine facies during rifting stage in the Zhu Ⅰ and Zhu Ⅲ Depressions of the Pearl River Mouth Basin shows that lacustrine facies spread much more widely in the Zhu Ⅰ Depression. It might be explained by the smaller extensional level of the Zhu Ⅲ Depression. The extensional level of a depression is affected by many factors, such as stress orientation, basement lithology and region faults. The differences of basement lithology, sag distribution, large potential fault below Cenozoic and sag-controlling fault orientation lead to the different extensional level of the Zhu Ⅰ and Zhu Ⅲ Depressions, and further control the different distribution of lacustrine facies.