Abstract：The stratigraphic age and sedimentary environment of the laterite bed in the Xihe basin have been studied in detail in the contexts of lithology, sporo-pollen assemblages and stratigraphic correlation and the geological evolution process during that time has been traced. The sporo-pollen assemblage in this area is the veld whose dominant elements are herbaceous Artemisia and subordinate elements are Pinus, Juglans and Graminae, of which Juglans and Ulmus are typical Paleogene-Neogene genera and species. Based on a comprehensive analysis of the lithologic and biological features, the authors think that the "laterite" bed in the Xihe basin belongs to the Pliocene Baogedawula Formation (N2b). In a plan view, the stratigraphic sequence type shows changes of the sedimentary environment from the river, alluvial fan and delta at the basin edge to the deep lake in the center of the basin.