There has been a great deal of disagreement about the closure time of the Hegenshan Paleo-ocean Basin in the Paleo- Asian Ocean. The Geleaobao syenogranite and monzogranite in Abaga Banner, Xilin Gol League, the middle of the Chaganaobao—East Ujimqin Banner tectonic magmatic belt, north and central Inner Mongolia, have important implications for revealing the closure time of the Hegenshan Paleo- ocean. Taking the Geleaobao granite as the research object, zircon U- Pb age, rock geochemistry and Hf isotope research were carried out to explore its formation age, rock genesis and tectonic environment. The study shows that the syenogranite and monzogranite were emplaced at 321. 3±2. 8 Ma and 306. 7±2. 4 Ma respectively. The rock is generally rich in SiO2, poor in CaO, MgO, P2O5, TiO2, moderate in K2O+Na2O, Al2O3 and Fe2O3T. It belongs to the high- potassium calc- alkaline series of rocks; enriched in light rare earths and trace elements such as Rb, Th, U, Zr, Hf, etc., deficient in heavy rare earths and trace elements such as Ba, Sr, Nb, etc., and have negative Eu anomalies; The zircon εHf(t) values of the two types of rocks vary from +7. 6 to +13. 1, corresponding to the two- stage model age of 511~928 Ma. Comprehensive analysis shows that the Geleaobao syenogranite and monzogranite were intruded in Late Carboniferous and belong to differentiated I- type granites. The rocks were formed in the island arc environment of the subduction zone and are the product of the subduction of the Hegenshan Paleo-ocean. The identification and determination of the Geleaobao Late Carboniferous arc magmatic rocks indicate that the Hegenshan Paleo- ocean Basin of the Paleo- Asian Ocean was not closed in the Late Carboniferous, but was in the process of northward subduction of the ocean.