The Chang 8 oilbearing interval of the Upper Triassic Yanchang Formation in the northwestern Ordos Basin was deposited in a stable tectonic setting and was mainly controlled by the northwestern sedimentary systems. During its deposition， shallow water delta was developed. The shallow water environment markers， such as coal seams， plant leaves and foots， worm holes， and so on， were widely distributed in the cores indicating the relatively shallow water during its deposition(several meters to over ten meters). The Chang 8 oilbearing interval was dominated by shallow water delta front subfacies and subaqueous distributary channel was the dominant microfacies. In comparison to the typical fluvialdominated delta， the delta in the study area is characterized by its wide distribution， the gently connecting of delta plain with delta front and prodelta on the plain with no obvious transition. The delta front can be divided into the inner front and outer front deposits. The sandbodies of the Chang 8 oilbearing interval were distributed to a long distance with larger scales and were characterized by podlike distribution along the channel direction and in vertical direction. The podlike sandbodies were distributed around the lacustrine basin. The distribution of the sandbodies is mainly controlled by the lake shoreline which is obviously different from the pattern of slope break belt controlling sandbodies in the depressional lacustrine basins.