Abstract: Northern Qilian mountain is one of a famous orogenic belts in Caledonides.It is mainly focused on formation and on underthrust-collsion and interactionental orogenic tectioncs of the main mountain-building period in the past reports.After the regional geological surveying at the western part of northern Qilian mountain, the author discovered a set of bedding detachment fault, ductile shear zone, flow cleavage and recum bent folds.In this paper, structure form, assembly, the characters of kinetics and dynamic and corresponding formation are analyzed and discussed in detail.Based on this, the authors pointed out all these are a synkinematic normal fault extensional structure group which are corresponding with the formation of rift basin in pre-orogenic phase.