Abstract: Xiaocaohu rock sheet developed in north of Dunhuang Group in Beishan Xiaocaohu area of Gansu Province, and the volcanic association exhibited sharply ductile deformation. Xiaocaohu rock sheet is similar to Permian volcanic association in terms of petrographic geomorphology, petrology and lithogeochemistry, and it belongs to rift-related volcanic rocks. Through LA-ICP-MS zircon U-Pb dating, we have obtained the isotopic age of 285±4Ma from the mylonitization dacite. The result proves that Xiaocaohu volcanic association is not a product derived from magmatism activities of Silurian but Permian, and it is a component of Carboniferous-Permian large igneous provinces in Tianshan area. The new information is of great significance to further study tectonic framework and evolution of Beishan area, Gansu Province.