Abstract: By two years' field work,the regional geological surveying and mapping on the scale of 1:50000 in Beipiao-Yixian district have achieved great progress.The research work shows that the Yixian Formation in Beipiao district may be lithologically subdivided into 4 members(in ascending order):1)the first member,including the basal conglomerate and intermediate-basic vol-canic rocks; 2)the second member,the lacustrine sedimentary rock member; 3)the third member,the upper basic volcanic rock member; and 4)the fourth member,with a base of conglomerate and graywacke with gravels,and middle-upper part consisting of acid-intermediate volcanic rocks and interlayer sediments(such as Jingangshan layer).Among them,the 2nd member contains abundant fossils of "Jehol Biota",including the precious and famous Sinosauropteryx,Confuciusornis,Archaefructus etc.Moreover,a lot of fossil dinosaurs are found recently in the 1st members.The discovery not only enriches the early fossil ele ments of the Yixian For-matrton,help the investigation on the living environment of the dinosaurs and the reason for their extinction,but also gives an important fossil evidence for determination of the age of Yixian Formation.