Objectives: The Baiyinhushu trondhjemite(belongs to Tonalite—Trondhjemite—Granodiorite series， TTG series) is newly identified in the Meilaotewula SSZ（Supra Subduction Zone）- type ophiolite of the Hegenshan (Hegen Mountains) suture zone, Inner Mongolia. TTGs are usually believed to result from the dehydration melting of subducted oceanic crust, to represent oceanic subduction and juvenile continental growth. However, whether the Late Carboniferous Paleo—Asian Ocean was still in subduction stage lacks further definitely petrological and chronological evidence and constraints. Therefore, this study carried out zircon LA- ICP- MS U- Pb geochronology and geochemistry on the Baiyinhushu TTG to discuss its origin, in order to provide new evidence for the tectonic evolution of the Hegenshan suture zone of the eastern Central Asian Orogenic Belt. Methods: Based on field geological surveying, petrology, geochemistry and LA- ICP- MS zircon U- Pb geochronology of the Baiyinhushu trondhjemite, this paper discusses the petrogenesis and tectonic setting of the trondhjemite, and the final closure time and subduction process of the Paleo—Asian Ocean. Results:The trondhjemite has high SiO2(66.50%~73.04%), Al2O3(15.11%~16.75%), Na2O (3.50%~6.16%),Sr(167.0×10-6~441.0×10-6) and low K2O(1.46%~2.38%),Y(5.30×10-6~9.51×10-6)contents, enriched in Ba, Sr large ion lithophile elements and LREE, and depleted in Nb, Ta, Ti, P high field strength elements and HREE. There is no pronounced Eu anomaly. The Baiyinhushu pluton belongs to high- Al TTG rocks and is similar to high- SiO2 adakites. The zircon U- Pb LA- ICP- MS dating shows that the Baiyinhushu pluton was formed at 309.2 ±1.6 Ma, indicating that the pluton emplaced in the Late Carboniferous, reflecting the TTG magmatism and juvenile continental growth of oceanic subduction zone in the Hegenshan suture at the Late Carboniferous. Conclusions:This study determines the Late Carboniferous (309.2 ±1.6 Ma) Baiyinhushu TTG, which was probably formed in island—arc setting of oceanic subduction zone and is arc magmatic rocks. The TTG might have been derived from the dehydration melting of subducted oceanic crust. The discovery and confirmation of the Baiyinhushu TTG in the Late Carboniferous provide new evidence for Paleo—Asian Ocean subduction and juvenile continental growth.