The Upper Triassic Bagong Formation in Dongqu area of the eastern Qiangtang Basin is mainly composed of dark fine clastic rock. The lithologic characters, sedimentary structures, probability cumulative grain size curves, grain-size parameters and C-M pattern of the sandstones of Bagong Formation in Dongqu outcrop profile all show as follows: the sandstones is generally fine and poorly sorted, the probability cumulative curve of the sandstones mostly represents one-stage, with a high percentage of the suspension and low percentage of the traction and saltation. In the C-M diagram, a line segment parallel to the C=M baseline is represented. The sedimentary structure of Paleodictyon trace fossils, which is flysch marks of deep sea-moderate sea, developed in Bagong Formation. Based on the comprehensive analysis, it is concluded that the Bagong Formation is a typical set of far-source fluxoturbidite in Dongqu area. Combined with the depositional characteristics of Bagong Formation in adjacent area, it is inferred that a palaeogeographic pattern of archipelago in Late Triassic developed in Qiangtang Basin.