The tuff at the intersection of Permian- Triassic in the western margin of Yangtze is of great significance in constraining the chronology of volcanic activity in the Emeishan Large Igneous Province and the magmatic arc around the Paleotethys. In this work, multi- layer tuff was found in the Late Permian Xuanwei Formation in the Yongshan area, western margin of Upper Yangtze. LA- MC- ICP- MS zircon U- Pb dating and Hf isotope study of the tuff at the bottom and top show that the weighted average age of the tuff at the bottom is 258. 9±0. 7 Ma, the zircon Th/Nb ratio is 2. 53~13. 05, the εHf(t) value is 3. 0~5. 0, and the TDM2 value is 988~871 Ma. Zircon trace elements, Hf isotope and two- stage model ages (TDM2) shows that its characteristics are related to the Emeishan basalt, and that it is a late product of the ELIP. LA- MC- ICP- MS zircon U- Pb dating and Hf isotope study of the tuff at the bottom and top show that the weighted average age of the tuff at the top is 254. 9±0. 6 Ma, the zircon Th/Nb ratio is 36. 50~311. 85, the εHf(t) value is -7. 4~-6. 9, and the TDM2 value is 1573~1529 Ma. Zircon trace elements, Hf isotope and two- stage model ages (TDM2) indicate that it was formed during arc volcanic activity in the Songma- Ailaoshan- Jinshajiang suture zone. The results show that the tuff at the bottom of the Xuanwei Formation is a product of acid volcanic activity in the later stage of the Emeishan Igneous Province. The volcanic activity of the Emeishan in the study area lasted until 258. 9±0. 7 Ma. Paleotethyan arc volcanism started at 254. 9±0. 6 Ma or earlier.