The Lhasa Terrane has undergone subduction, subtraction and land- land collision of the New Tethys Ocean, and a large area of intermediate- acid intrusive rocks has emerged, providing favorable conditions for study of crustal evolution. The genesis and dynamic background of the Late Triassic- Early Jurassic magmatism in this area are still controversial. To solve these problems, this paper studies the Qieqiong syenogranitic granite in the middle south region of Lhasa Terrane. The samples are analyzed by petrography, zircon U- Pb geochronology, Hf isotope and whole- rock geochemical characteristics, and its petrogenic characteristics and tectonic significance are discussed. The Qieqiong syenogranitic granite is mainly composed of quartz, potassium feldspar, plagioclase and biotite. The U- Pb weighted mean age of magmatic zircon is 210. 28±0. 92 Ma (MSWD=0. 99) indicating formation in the Late Triassic. The rock is characterized by high SiO 2 (73. 44%~75. 76%), high K 2O (4. 87%~5. 15%) and high Al 2O 3 (12. 58%~13. 40%). The Al saturation index (A/CNK) is more than 1. 0 indicates that it belongs to peraluminous high K calc- alkaline S- type granite. Light rare earth elements are relatively enriched and have moderate negative europium anomalies. Trace elements are enriched in K, Rb and radioactive elements U and Th of large ion lithophile elements, and depleted in elements Ba, Nb, Sr, Ti, Zr and Hf to varying degrees. The ε Hf ( t ) shows a low negative value (-4. 2 to -2. 6), and the Hf two stage mode age was between 1262 Ma and 1347 Ma. The syenogranitic granites were formed in a post- collisional extensional tectonic environment and were the product of partial melting of argillaceous sediments in the crust. At the end of Middle Permian, collision orogeny occurred between the southern margin of middle Lhasa terrane and the northern margin of Australia, which resulted in the closure of the Songdo Tethyan Ocean and subsequent post- collision magmatism, forming the Late Triassic granite belt near the north latitude of Lhasa Terrane at 30°N。