Abstract: Badain Jaran Desert is the third largest desert of China and also is the only desert in which megadunes distribute densely. The desert also develops hundreds of large and small lakes. The paleoclimatic and paleoenvironmental researches on the lake sediments are of significance for the further study on the formation mechanism of Badain Jaran Desert，etc. As the research object in this paper，Barunbaoritaolegai profile is the relatively typical one amomg these sedimentary outcrops which are located in the southeast of the Badain Jaran Desert. In previous studies，researchers had presumed the age of the sediment to the early Pleistocene. However，the detailed research on sedimentary outcrop has not been done. To ascertain paleoenvironmental evolution of southeast edge of the Badain Jaran Desert，this paper selects the representative Barunbaoritaolegai outcrop deposits as the research object. By combining modern lakes core and using the analysis methods of C-M figure，the frequency curve，the cumulative frequency curve，grain-size parameter，grain composition，and combing the results of OSL and ¹⁴C dating data，the authors carry out research on the Barunbaoritaolegai profile. Results show that combined with chronological data，the grain-size characteristics can reflect the change of the ancient environment in the study area well. According to the graph of the ages and grain-size parameters of Barunbaoritaolegai，the paleoenvironmental evolution which is reco- rded by the profile can be divided into three stages: the stage of the warm and wet climate during 106～93.65 ka BP，the stage of the dry and cold climate during 93.65～87.93 ka BP and the stage of the warm and wet climate during 87.93～81.98 ka BP. The comparative analysis of the C-M graph between Barunbaoritaolegai profile and modern lakes core indicates that the Barunbaoritaolegai profile belongs to the lacustrine deposit. The Barunbaoritaolegai outcrop is most probably a lakeside highland or an island in a lake which came from the continuous development of Barunbaoritaolegai lake. In addition，the analysis result indicates that the Badain Jaran Desert had developed lakes which are larger than today's during the last interglacial period，that the lake had experienced the warm periods of MIS 5a and 5c and cold period of MIS 5b，and that the results are consistent with those of the northwestern region in the last interglacial northwest. Furthermore，by the analysis on the characteristics of frequency curve and cumulative frequency curve，the authors find a breakthrough clue，that is the Barunbaoritaolegai profile deposits are likely to be the basement of the desert，which is of great importance for investigating the age and the formation mechanism of Badain Jaran Desert．

Key words: the last interglacial period, paleoclimate environment, characteristics of grain-size, Barunbaoritaolegai, Badain Jaran Desert