Based on the measurements of the Upper Triassic Xiaotangzi Formation (T3t) at Hanwang of Mianzhu and Hejiawan of Guangyuan, this study analyzed its sedimentary environments and facies in details. The Hejiawan T3t is attributed to shallowwater environments: shoreface bar, shelf mud, intertidal flat and wavedominated delta. The Hanwang T3t is especially characterized by deepwater faces: shoreface bar, gulfmud, medialramp channel and slumping sheets, and delta deposits. Preliminary study of pyrithe nodules collected from the Hanwang profile was also preformed. On the whole, the Xiaotangzi Formation is believed to correspond to the sedimentary model of sandmud rich ramps. It can be pointed out that the deepwater mudstone at the middle part of Hanwang profile should mark the active thrusting tectonism of Longmenshan while the thick sandstone bodies of HST to lower part of the 2nd Member of Xujiahe Formation might deposit in the quiescence period of Longmenshan tectonic activity. This study suggests that the basal shoreface sandstone body of T3t is of highly potential for natural gas exploration.