Objectives: There are abundant magmatic rocks in the south of the Central Asian orogenic belt, recording the Neoproterozoic to Permian subduction of the Paleo- Asian ocean. However, there is still no uniform understanding of the final closing time. Based on the study of Qianhuhetaolegai intrusion in the Bainaimiao island arc, this paper provides a further constraint for determining the time limit. Methods: Five fresh samples were collected for analyzing the whole- rock main and trace elements in Qianhuhetaolegai of Zhengxiangbai Banner. One sample was selected to carry out the zircon U- Pb dating study by LA- ICP- MS method. The determination of major elements, trace elements and rare earth elements in chemical analysis samples was completed in the laboratory of Beijing Yanduzhongshi Testing Technology Co., Ltd. The sample was pretreated by digestion method, and the content of trace rare earth elements in whole rock was determined by inductively coupled plasma mass spectrometer (ICP- MS) M90. The precise analysis of the main elements of rock was carried out by XRF fluorescence spectrometer melting method. The test was performed using LA- Q- ICP- MS. The laser ablation system was New Wave UP213 and ICP- MS was Bruker M90. The zircon dating area was selected according to zircon photomicrography, and the diameter of the ablation spot was selected to be 30 μm. The isotope ratio correction was performed using the Andersen method. The U- Pb age, Pb isotope ratio and trace element content in zircon dating were processed using the ICP- MS DataCal program, and the weighted mean age calculation and mapping were performed using the Isoplot program.Results: Based on the study of the field occurrence characteristics, microscopic characteristics, geochemistry characteristics and chronological characteristics of the intrusion, the lithology and rock types were identified in detail, its emplacement age was determined, and its origin and tectonic background were discussed. Zircons collected from the intrusion exhibit zone texture and have high Th/U ratios of 0.37 to 0.69, consistent with magmatic zircons. LA- ICP- MS zircon U- Pb dating revealed that the intrusion was emplaced in the middle Permian (276.4±1.5Ma). All the samples are enriched in SiO2 (70.99% to 71.78%), alkalis contents (7.32% to 8.08%), with high K2 O/Na2O ratios (0.73 to 0.95). They are enriched in LREEs relative to HREEs, with (La/Yb)N= 11.89 to 13.59 and slightly negative Eu anomalies of 0.69 to 0.76. All the samples are relatively enriched in LILEs (e.g., K and Rb) and depleted in HFSEs (e.g., Nb, Ta, P and Ti). Conclusions: The Qianhuhetaolegai biotite granite was emplaced in the middle Permian. The Elemental data suggest that the intrusion belongs to I- type granite and was derived by partial melting of crustal source induced by subducted slab- released fluids. Thus, the intrusion was likely emplaced in an active continental margin. We consider that the final collision between two paleo- plates in the study area should not be earlier than 276.4 Ma.