Abstract: In arid and Semi-arid areas,the locally isolated flood events can not be collected efficiently due to the rare hydrological stations density.Since the 1970s,a lot of simple flood investigating site-fixed on rivers in a broad region have been set up to record the annual maximum discharge in Gansu province and Ning xia Hui Auto nomous regions.A new statistical approach suitable for this kind of data has been put forward in this paper.The statistical region of which is a district with many stations.The design flood for the given site can be obtained through the frequency transformation from area to point.A case study shows the successful application of the proposed method to the upper reach of the Jinhe River basin in Gansu province,and several problems have beed discussed.