The middle and late Permian faunas from the west Qinling Mountains have suffered a replacement event during the developing history. It behaves that the fusulinids occurring from the bottom of the late Maokouan Dieshan Formation of the middle Permian were sharply reduced or disappeared, and the brachiopods were prosperously developed. The fusulinids are well developed in the middle Maokouan Reranggou Formation, such as Afghanella and plenty of Parafusulina, Chusenella. But from the very beginning of the superjacent Dieshan Formation, only a small amount of Parafusulina, Chusenella and Schwagerina appeared intermittently, and meanwhile a small brachiopods fauna, represented by Urushtenia and Neoplicatifera, and small solitary tetracorals alternately occurred. This fauna replacement event was under the control of the variations of sedimentary environments and regional tectonic activities. The sedimentary environments of the Dieshan Formation was changed from the early shallow water of open platform into stagnated water of semi-restricted platform, and thus resulted in disappearance of fusulinids and flourish of small brachiopods. The change of sedimentary facies and the replacement of faunas are well inosculated in stratigraphic horizon. The study area is located on the west margin of the carbonate platform or the carbonate platform margin of the late Hercynian rift zone in the west Qinling Mountains, so both of the changes of sedimentary facies and the replacement of faunas must be influenced by regional rift activities. Based on biostratigraphic study in this area, it is definitely known that the Permian rift activity of this region started at the late chron of the middle Permian Maokouan Afghanella schencki (or the late chron of Neoschwagerina), and finished before of the late Permian Changxingian Palaeofusulina.