Abstract: The sedimentary environment, deposition epoch and tectonic environment type of Tongshan Formation as well as the early Paleozoic sedimentary records of Xing'an stratigraphic region constitute an important window to study the early stage tectonic evolution of Xing-Meng orogenic belt. The authors studied Ordovician Tongshan Formation exposed in the Wayao area of Dong Ujimqin Banner in Inner Mongolia. Sedimentary sequence, sedimentary facies and features of sediments indicate that Tongshan Formation is terrigenous clastic turbidite. LA-ICP-MS zircon U-Pb dating of volcanic tuff sampled from Tongshan Formation yielded the depositional age of 458.5±2.6Ma for the first time in Inner Mongolia and restricted its age between late Middle Ordovician and early Late Ordovician. Geochemistry of the detrital rocks shows that the tectonic setting of the provenance for the Tongshan Formation is mainly charac-terized by the Active Continental Margin (ACM) and Continental Island Arc (CIA). Combined with the regional geological data, the authors infer that the Tongshan Formation was formed by the turbidite fan in a active continental margin tectonic environment.