In this paper, the fundametal characteristics of the geological structures of the Hexi corridor basin and the recently active features of the fault at the northern flank of the yumushan mountain and Shanglongwang fault at the eastern flank of the yumushan mountain in its middle segment have been discussed. The research result has indicated that
(1) The Qilian mountain range is a nappe that moves to the northeastwards. It is estimated that the distance moving to the northeastwards is abont 4-5 kilometers since the middle Pleistocene.
(2) The NWW fault belt located at the north flank of Yumushan mountain takes overthrust as the dominant factor and cuts the deposits of the later part of the late Pleistocene.
(3) The activity type of the NNW Shanglongwang fault belongs to the type of the right strike slip accompany with the pressure. The geologicol and micro geomorphic evidences show that there have occurred 4 times earthquakes with the magnitude 7-8 in this fault since 25000yr. ago, and the latest one of them occurred at about 13300yr. ago. About the reoccurrence interval of the 4 times paleothquakes, they are nonuniform, namely, there are either the big or the small interval in this fault.