Abstract: The chemical alteration index method is an economic, practical and effective method for recovering the weathering history and sediment flux of the source area. The research on provenance feature of Liwan Sag, Pearl River Mouth Basin (PRMB), has been insufficient. In this paper, the weathering history and sediment flux of source area during late Oligocene to early Miocene were restored by analysis of chemical alteration index (CIA) based on the core data. In addition, their influence on depositional filling in the study area was also discussed. The results show that the source area during late Oligocene in the study area experienced a strong weathering stage, and the abundant sediment supply in this period constituted one of the important controlling factors for the rapid progradation and spectacular scale of shelf margin delta and gravity flow depositional systems in the northwest of the study area. On the other hand, during the early Miocene, the weathering of NW provenance area weakened and the sediment supply was reduced, but the sediment supply in the eastern area was more sufficient than that in the western part. It is shown that, in addition to the main provenance from the northwest, the local provenance had an important influence on the depositional infilling pattern during the early Miocene. It is inferred that the sudden resurrection of the eastern provenance, i.e., the Eastern Paleo-uplift and the Xingning Uplift, constituted one of the important control factors for the formation and development of the early Miocene grooves in the eastern area. In the study of sediment source area in the ultra-deep water area, the semi-quantitative method of CIA has certain indicative meaning for the determination of local provenance in basin.