Objectives：The Tanjiawan section in Bairin Left Banner of Inner Mongolia located in the Xing′an—Mongolian Orogenic belt, North China.Combined with petrological study, LA- ICP- MS U- Pb zircon age and palynological study of the section, we could determine the stratigraphic age and analyze the provenances of the red- layer detrital rocks with the typical features of sediment associations and discuss the possbile geological significances. Methods：Based on the data of the Tanjiawan section measuring, through the regional stratigraphic correlation, the LA- ICP- MS U- Pb detrital zircon dating and rare earth element test analysis of the sandstone sample from the lower part of the section, the identification of the sporopollen fossils within the siltstone from the same horizon as the sandstone sample, and the provenance analyses. Results：The strata of the section were corresponding to the middle and low parts of the Xingfuzhilu Formation, through the regional stratigraphic correlation. The LA- ICP- MS U- Pb detrital zircon dating gained the youngest age of 244 Ma and the youngest peak ages of 268Ma.The composition and distribution characteristics of concordant ages of detrital zicrons from the sandstone sample suggests the multiplicity of the provenance of the section. Conclusions：The deposition time of the middle part of Xingfuzhilu Formation of the section ought to be later than 244Ma. Combining the identification of the sporopollen fossils, it could be speculated that the deposition time of the middle part of Xingfuzhilu Formation of the section was Middle stage of Middle Triassic. Combining the relevant data of the regional structure and Zircon U- Pb dating, it could be speculated that the provenances were consisted of the Paleozoic magmatic rocks in the area around Sonid zuoqi—Xilinhot— Xi Ujimqin Qi, the granites or granitic gneisses of Middle Permian to Middle Triassic in Linxi area, and the Early Paleozoic magmatic rocks in the northern margin of North China Plate.