Abstract: Yuejin No.2 oil reservoir includes three main oil groups:Xiayou shashan Formation(N₂¹), Shangganchaigou Formation(N₁),and the lower part of Xiaganchaigou Formation(E₃¹)For a long period of time,it has been considered to be a general braided river delta,with the main types of sand stone being distributary channel,mouth bar,and sand sheet.In our study,through the core observation,log-phase analysis,and in accordance with the sediment grain size,sand body,and the spatial distribution patterns of modern riversediment type,the deposition background of the districtis still braided river delta,but the sedimentary microfacies types and causes of sand body model are different from the general braided river delta,which is that the skeleton of sand body is characterized by diversion dams,diverting rivers,and estuaries due to dam development.