Abstract: In the northern margin of West Qinling, there not only developed a series of inherited multiple active or new-born near EW trending faults, but also a series of NW-trending sinistral strike-slip faults in the Oligocene-Miocene strata which are inconsistent with the archly near EW-trending regional faults and have unique structural characteristics. These NW-trending sinistral strike-slip faults do not develop the typical tectonic phenomena that generally developed in brittle faults, such as fault breccia, grinding conglomerate, crushed powder rock, gouge, slickenside, striation, fault step and so on, and only shows a certain width of lenticular zone and the stratigraphical twisted zone by shear pull-apart or strata rotation. Furthermore, between two NW-trending sinistral strike-slip faults developed 1 km wide stratigraphic twist zone which is similar geometrically to kink structural configuration on horonzontal plane. This faults transected the Oligocene-Miocene strata, and was covered by Pliocene conglomerates and cut by near EW-tending sinistral faults since the Quaternary, which indicate that the faults formed after the Oligocene-Miocene and before late Pliocene, i.e., the Early Pliocene. The NW-trending sinistral strike-slip faults, a new type of fault in the north margin of West Qinling, do not have the characteristcs of typical brittle faults and its sinistral strike-slipping formed stratigraphic twist zones which is similar to kink-fold geometric configuration, indicating that the deformation has the characteristics of ductile-brittle transition and slow shear deformation. Therefore, the formation mechanism of this kind of fault is the upperward propagation of the large scale sinistral strike-slip ductile or ductile brittle shear zone in the basement or middle-lower crust into the upper sedimentary cover strata, which imply that the NW-trending faults and stratigraphic twist zones formed by fault’s sinistral strike-slipping in the Upper Cenozoic sedimentary cover are just the passive structural responses to NW-trending sinistral ductile shear zone in the basement or middle-lower crust. The NW-trending ductile shear zone in the basement or middle-lower crust may indicate the tectonic indicator of SE-directed flowing of the deep ductile crustal material to along the northern margin of the West Qinling during the Early Pliocene , representing the transformation of the deep crust shortening-thickening to the lateral expansion of the crustal ductile matter. This special type of fault is of great scientific significance to the understanding of Cenozoic tectonic deformation regime transformation and crustal uplift in the northeastern margin of Qinghai-Xizang Plateau.