Abstract: Baiyun Sag is an important oil and gas producing area in the Pearl River Mouth Basin. At present, research of Baiyun Sag is mainly in the main body of the sag, while it was understudied in the western Baiyun subsag. In recent years, the oil and gas exploration in the subsag has been intensified, and the drilling has been carried out in the hanging wall and foot walls of Panyu 25 Fault. To further explore the exploration potential of the subsag, the differential accumulation between the hanging wall and foot wall was analyzed and the hydrocarbon accumulation rule in this area was discussed. Based on the PVT (pressure, volume, temperature) characteristics of samples, the MDT (mini drill stem testing) pressure analysis, natural gas composition, carbon isotope characteristics, and paleotectonic analysis of accumulation period, it is concluded that Panyu 25 fault has strong segmentation, and the hanging and foot walls are two independent blocks in the key accumulation period, showing different hydrocarbon accumulation. Geochemical analysis of hydrocarbons showed that the condensate gas in the up-thrown side came from Baiyun 3 subsag, while the oil and gas in the down-thrown side originated from the adjacent Panyu 25 subsag. The accumulation rule of the western Baiyun subsag was clarified, which is beneficial to the exploration and deployment of this area. The natural gas exploration should be carried out around the dominant migration path of Baiyun 3 subsag, and the crude oil exploration should also be conducted around the proximate source of Panyu 25 subsag. This study provided a useful reference for the research on the differential accumulation of the hanging and foot walls of faults in other areas.