It is an important period for the tectonic evolution of the eastern segment of the Central Asia Orogenic Belt during the Late Permian to Middle Triassic, which involved the final closure of the PaleoAsian Ocean and the sharp changes of sedimentary environment. The well exposed Upper Permian Linxi Formation and LowerMiddle Triassic Xingfuzhilu Formation record the evolution history of southeastern Inner Mongolia. Then, sandstone samples were chosen to carry out UPb and LuHf isotope test, which is used to analyze the geochronology and extract sediment provenance information. The new UPb data show the red stratum which was considered as the symbol of Triassic before is also discovered in Late Permian, southeast of Linxi county. In addition, the previous Early Triassic Xingfuzhilu Formation is probably an Early to Middle Triassic sedimentary sequence, which is conformable contact with lower Linxi Formation. Furthermore, an age gap between Early and Middle Triassic was found base on both geochronological data and field observation. The geochronological results also show that sandstones from Linxi Formation have four groups of UPb age at 254~336Ma, 372~528Ma, 669~1000Ma, and 1300~2534Ma. The εHf（t）values range from -25.6~+17.2. In contrast, samples from Xingfuzhilu Formation only have one group of UPb age at 241~278Ma, while the εHf（t）values range from +8.6~+16.5, and few Carboniferous and Paleoproterozoic detrital zircons were found. In view of different characteristics of UPb and Hf isotope, the sandstones from Linxi Formation probably sourced from XingMeng Orogenic Belt and north of the North China craton, while the sandstones from Xingfuzhilu Formation mainly sourced from surrounding magmatic rocks. These results, combined with regional data, indicate that the final closure of the PaleoAsian Ocean is before Late Carboniferous. Since then, the sediments and magmatism happened in an intracontinental environment.