Abstract：Volcanic rocks in the Upper Triassic Xiaodingxi Formation in the Shiden-Tue area belong to the Triassic volcanic belt along the banks of the Lancang River in western Yunnan. The author has made a systematical and comprehensive study of the petrographic, petrochemical and geochemical characteristics of the volcanic rocks and determines the tectonic environment of these rocks from a theoretical angle. The study shows that these volcanic rocks are composed dominantly of andesite with subordinate basalt, belonging to the calc-alkaline series, and formed in the island-arc tectonic environment.