Abstract: The detailed study of the sedimentary facies in Yuejin 2 area of northwest Qaidam is of great significance to the exploration of oil, gas and uranium deposits. On the basis of the data from more than 200 typical boreholes in northwest Qaidam,the regional palaeogeography and tectonic features,and the iso thickness map of the sand body,the authors have drawn the plane maps of sedimentary facies for upper Youshashan Formation, Shizigou Formation and Qigequan Formation in this area, revealing that braided river delta front, fan delta plain, braided river delta plain, beach bar,fan delta front,flood-flood plain,and shore shallow lake developed in the late Cenozoic in northwest Qaidam.Through comprehensive analysis of lithology,color,sedimentary sequence, logging curve, and the sedimentary structure of ZK8-20, ZKII5-21, ZKII1-10, Yuejin II4-11, Yuejin II2-6 and other boreholes in Yuejin 2 area, it is considered that braided river delta plain mainly developed in upper Youshashan Formation and Shizigou Formation of this area,showing the sedimentary characteristics of distributary channel above water and among distributary channels.The Qigequan Formation is mainly developed the differentiation river delta front, characterized by underwater distributary channel, distributary bay and mouth bar.The late Cenozoic sedimentary facies are mainly characterized by regressive distribution in the study area. The lake level slightly decreased in Shizigou Formation and rose in Qigequan Formation. Littoral-shallow lake subfacies, discerned river delta plain subfacies and discerned river delta front subfacies developed vertically from top to bottom, forming the sedimentary model of upper lacustrine facies and lower discerned river delta facies.