Abstract: In this paper, detrital zircon U-Pb ages were studied with the aims to reveal the formation ages and associated tectonic settings of clastic rocks from Linxi Formation in the north Xilamulun River, Balinyouqi, Inner Mongolia.The LA-ICP-MS results show that the 98 zircons grains show concordant ages of 252~315 Ma, 376~523 Ma, 752~1097 Ma, 1465~1694 Ma and 1833~2563 Ma.The youngest zircons age is 252 Ma, which indicates that the lower sedimentary age of the Linxi Formation is the Late Permian.The zircon age spectrum map, which includes the age information of both the southern margin of the Central Asian Orogenic Belt (CAOB) and northern margin of the North China Craton (NCC), showt that the stratum was characterized by multi-sources.This indicates that the materials in the Linxi Formation was mainly sourced from the south margin of the CAOB with minor from the northern margin of the NCC.The sample age information and the previous Paleontological stratigraphy and Paleomagnetic studies indicate that the sedimentary time of the Linxi Formation is the late Middle Permian to early Early Triassic, with the main sedimentary time of Late Permian.Combined with the comparison of regional strata and tectonic evolution in the eastern CAOB, the authors conclude that the Paleo Asian Ocean was likely final closed during the Late Permian.