Abstract: The sedimentary facies analysis is fundamental to all the palaeoenvironmental, palaeoclimatic, and palaeogeographic interpretation in the reconstruction of sedimentary facies and palaeogeography. The present paper gives a detailed description of lithology, basic sequence, sedimentary facies and vertical sedimentary evolution of the Oligocene Rihongla Formation in the Chejiaco area, Ngamring, Xizang. The Rihongla Formation consists dominantly of a succession of purplish red terrigenous siliclastic rocks including conglomerates, sandstones, siltstones and mudstones which are indicative of a typical fluvial sedimentary environment. The channel subfacies in this Formation may be subdivided into the channel bar, point bar and channel lag microfacies, and laid down in the mountainous areas to alluvial plains during the Oligocene.