Abstract: Abundant fusulinds were found in Upper Carboniferous-Lower Permian strata in the northwest of Tarim Basin. Four fusuline zones were recognized, namely Pseudostaffella zone, Profusulinella zone, Fusulinella-Fusulina zone and Pseudoschwagerina zone in upward succession, which can be well correlated with those from South China and Darwaz area of Pamir. It is indicated that Biegentawu Formation is Luosuan stage to Dalaun stage of Pennsylvanian in age, while the upper member of Kangkelin Formation belongs to the Late Carboniferous Xiaodushanian stage to Early Permian Zisongian stage. It is also inferred that the boundary between Carboniferous and Permian lies at the bottom of the 71st layer, as evidenced by the fusulind Pseudoschwagerina. The authors also hold that the late Pennsylvanian stage witnessed the sea regression with the addition of the paleotopographic factor, resulting in the stratigraphic gap of Triticites zone.