Abstract: Overpressure,which is closely related to the generation,migration and preservation of hydrocarbon,JP plays an important role in petroleum accumulation dynamics. This paper confirms the existence of overpressure in the Panyu 4 sag, Pearl River Mouth Basin based on logging, drilling, geological and geochemical data, discusses its forming mechanism, divides the area of overpressure, and reconstructs pressure evolution process in a two-dimensional framework. It suggests that overpressure, which is mainly controlled by lithology, exists widely in Panyu 4 sag.Its forming mechanism includes both hydrocarbon generation and the compaction disequilibrium.The history of pressure evolution is complex. Overpressure in Wenchang Formation includes two stages:the eaily stage is due to compaction disequilibrium,and the later stage is related to hydrocarbon generation since 15 Ma.