Abstract: During the 1∶50000 regional geological and mineral resources survey in Akqi County, Karaqi Formation was established as a lithostratigraphic unit. Karaqi Formation is mainly composed of deep-water carbonate sediments, obviously much different in lithology, rock assemblage and paleontological assemblage from Kangkelin Formation distributed in south area and comprising carbonate platform sediments. It is indicated that the age of Karaqi Formation should be Late Carboniferous-Early Permian, as evidenced by an analysis of paleontology and Triticites and Pseudoschwagerina Zones built here. Therefore, the two formations distributed in different areas should belong to simultaneous sedimentation with different facies. The establishment of Karaqi Formation facilitates the improvement of the Upper Carboniferous-Lower Permian stratigraphic system and also confirms the existence of Upper Carboniferous-Lower Permian platform margin slope zone in this area. The results obtained by the authors are of great importance for the study of the Upper Carboniferous-Lower Permian lithofacies paleogeography in northwestern Tarim region.