The Member 3 of  Paleogene Shahejie Formation  is the main petroliferous interval in the Bonan Sag of Jiyang Depression in Bohai Bay BasinCurrently the viewpoints about the sedimentary facies types are quite different. The sedimentary gradients of each sandy interval of the Member 3 of Shahejie Formation were calculated by applying the spatial analysis module of geographic information system ArcView GIS 3.2 aThe sedimentary gradient of the  9th sandy interval  is mainly between 1.5°～3.5° and the gradient where it is adjacent to the Gudao Uplift can reach 3.5°～5°，while the sedimentary gradient of the 5th sandy interval  is generally less than 1.8°According to the representative features of these two sandy intervals，the depositional and tectonic setting of the basin，the sedimentary characteristics of the mudstones surrounding the reservoir sandbodies，the vertical sedimentary assemblages，the planar distribution of the reservoir sandbodies and their own sedimentary characteristics，it is concluded that the main reservoir sandbodies of the Member 3 of Shahejie Formation in the Bonan Sag is dominated by braided fluvial deltaic deposits and only the 9th sandy interval at the basal part of the Member 3 is of deepwater turbidite origin.