The Lower Cretaceous Takena Formation in the Linzhou basin, Lhasa terrane was deposited in the back- arc extensional setting during northward subduction of the Neo- Tethys oceanic lithosphere to Lhasa Terrane, which is of great significance for reconstructing the palaeogeography of this period and understanding the control of extensional setting on sedimentation. Based on field outcrop descriptions and thin section observations, the stratigraphic architecture, petrology and paleontology characteristics of the Takena Formation are studied, and the sedimentary evolution and characteristics in the extensional setting during the Takena period are discussed by comparing the coeval Arabian Plate Shuaiba Formation deposited in the passive continental margin of the Neo- Tethys Ocean. Four lithologic members are identified in the Takena Formation from bottom to top according to the lithological association of ten rock types of clastic, siliciclastic- carbonate mixed and carbonate rocks, witch record a third sequence stratigraphy composing of transgression- regression cycles. The lithofacies change from sandstone, siliciclastic- carbonate mixed rocks to carbonate rocks, combined with sedimentary structures and fauna typify the sedimentary environment of the 1st member of the Takena Formation (K1t1) as a lagoon in intertidal- subtidal zone. Subsequently, the relative sea- level rose sharply and thick marl deposited in K1t2 indicating palaeobathymetry below the storm wave base. The storm- induced shell concentrations intercalated in calcareous shale were first identified in K1t3 in West Maxing Section and changed into shoal facies to the southwest indicated by bioclastic and oolite grainstones in the East Jiarong Section. Relative sea- level continued to drop leading to the end regression, and the coastal and floodplain environment siltstone intercalated in shale were deposited in K1t4. Comparison between the coeval Takena and the Arabian Plate Shuaiba Formations shows similarity between the fauna types indicating that the Linzhou Basin, southern Lhasa Terrane was connected with the Neo- Tethys Ocean in the Takena period. Under the extension setting in the active continental margin, sedimentation is characterized by rapid differential subsidence of the basement and continuous input of terrigenous sediments, which led to rapid vertical and lateral facies transition, development of siliciclastic- carbonate mixed rocks, and the absence of shallow clean- water- preferred organism rudists and Lithocodium- Bacinella and deep- water plankton.