Abstract: The first discovered Late Triassic strata was introduced in terms of its petrological and biostratigraphic characters in the paper.The upper Triassic was only distributed in Wuqia-Kusilapu fault depression,which was belonged to a different protobasin comparing with the southwestern foreland basin.This is important for analysis of structural evolution and evaluation of hydrocarbon potential in the southwes tern Tarim depression.