Rock assemblages, trace elements and mineralogy of volcahic rocks along the Lancangjiang belt in southwest Yunnan show that these rocks have the main properties of shoshonite series. According to their geological, Petrological and geochemical characteristics, they are believed to be intracontinental arcvolcanic rocks. The K2O-,Al2O3-rich rhyolitic volcanics of Middle Triassic Manghuai Formation belong to collision type arc-volcanic rocks, while the K2O-high salt-shoshonite-latite of the upper Triassic Xiaodingxi Formatiom and the bimodal type volcanics assemblage of potassic trachybasalt-K2O-high rhylite of Manghuaihe Formation are of lag-type arc-volcanic rocks.