In this article, zircon U- Pb dating, Hf isotope and geochemistry of the Agashiaobao monzogranite in the eastern Junggar, Xinjiang were carried out. LA- ICP- MS zircon U- Pb dating for monzogranite yields a late Devonian age of 372. 1±1. 5 Ma (MSWD=0. 22). Geochemical analysis shows that the monzogranite is characterized by high contents of SiO2 (70. 7%~71. 7％) and K2O (3. 93~4. 33％), K2O/Na2O of 1. 00~1. 17 with the A/CNK of 1. 01~1. 04 and low 10000Ga/Al(1. 81~1. 90), sugguesting that they belong to high- K calc- alkaline I- type granite. The monzogranite displays enrichment of LREEs and LILEs (i. e. Baand Sr) and depletion of HFSEs (such as Nb, Ta and Ti), indicating that it may be influenced by subducted material. High εHf(t) (11. 2~15. 2) and young Hf two- stage model age (388~554 Ma), as well as high Zr/Nb ratio of 7. 46~8. 24 and high Th/Ce ratios of 0. 16~0. 55, suggest that it may derive from partial melting of juvenile lower crust. The high- K calc- alkaline I- type granite has low contents of Ta (1. 60×10-6~1. 79×10-6) and Y (1. 41×10-6~1. 67×10-6). Rb- (Y+Nb) and Yb- Ta classification diagrams show that the monzogranite falls in the VAG area, indicating that it formed in an island- arc enviroment. Therefore, combined with regional tectonic and sedmentary evidence, this study concludes that the East Jungger area was in an island- arc setting related to subduction in late Devonian. Late Devonian ocean- ridge subduction and slab window formation played an important role in the formation of various rock assemblages in eastern Junggar at the same period.