East Kunlun hosts large- sized intermediate- acid intrusive rocks, providing a natural laboratory for the study of continental crust growth. However, the tectonic setting of granite formation and the evolution processes of Paleo- Tethys belt of East Kunlun remains controversial. In this paper, we carried out a detailed investigation on the Zhamaxiuma syenogranite from the eastern segment of East Kunlun using zircon U- Pb dating, whole rock geochemistry and Hf isotopes in order to identify the formation time and petrogenesis of rocks, and provide basis data for the evolution of regional tectonics. Syenogranite consists mainly of plagioclase, alkaline feldspar, quartz, biotite, with minor amount of hornblende. Zircon U- Pb dating yields an age of 240.3±1. 8Ma, indicating its emplacement in Middle Triassic. The syenogranite is geochemically characterized by high SiO2 (70.36%~71.20%) and Al2O3 (14. 06%~14. 18%), relatively rich in alkali with Na2O+K2O (7.52%~7.89%), low TiO2 and MgO, enriched in large ion lithophilic elements Rb, Ba, Th, etc, depleted high field strength elements such as Nb, Ta, Ti, etc. The rock belongs to high K Ca- alkaline and metaluminus- weak peraluminous I- type granite. εHf(t) values range from -4. 1 to +2. 3, and TDM2 ages between 1126 Ma and 1536 Ma，indicating that the syenogranite originated from partial melting of Middle Proterozoic crustal materials. The integrated analyses show that the syenogranite probably formed in the active continental margin and was the product of transformation from subduction of paleo- Tethys Ocean in East Kunlun to collision.