The Bikou terrane lies at the junction of Qinling orogenic belt, SongpanGarze orogenic belt and Yangtze Plate. Three tectonstratigraphic units have been identified within this terrane: ① the Neoproterozoic basement complex, composed mainly of volcanic rocks of Bikou Group and turbidite of Hengdan Group, has weak deformation in the core but strong ductile shear deformation along the margin. The basement is separated from its overlying strata by a detachment fault composed of ultramylonite. Metamorphic grade ranges from blueschist facies to lawsonitealbite chlorite facies within the basement complex. ② the Paleozoic middle ductile slab is composed of SilurianDevonian mylonite and phyllonite, in which develops three stages of foliations (S1, S2, S3). The middle ductile slab underwent metamorphism of midgreenschist facies. ③ the Mesozoic sedimentary cover, including Triassic Guanjiagou Formation to the north of Bikou terrane and JurassicCretaceous in some small areas, is characterized by brittle fault and fracture belt without metamorphism. The geometry and kinematics features of up totheSSE shear within the detachment fault and strata prove that regional extension collapse developed in Bikou area in Mesozoic, 206~154Ma. In conclusion, detachment fault and middle ductile slab resulted from the regional extension during the Mesozoic orogenesis in SongpanGarze, which caused thinning and selective removal of the strata, as well as the uplift and exhumation of the basement complex in the hinterland of orogenic belt.