Abstract: The micro-facies are uncertain and their distribution characteristics are not fine, which exists in the sedimentary study of YuejinⅡ oilfield that locatedatthe west part of Qaidam Basin. And such problems restrict the fine development at the high water-cut stage.So based on the basic principle of sedimentology, the delta plain, braid-river delta front, shore-shallow lake sedimentary background in early-Oligocene have been elaborated by synthesizing geological facies identification(e.g. petrology marks and sedimentary tectonics marks) and logging facies analysis(e.g. and SP curve character).Such sedimentary sub-faciesare divided into ten micro-facies, such as water distributary channel and flood plain, underwater distributary channel, mouth bar, distal bar, sheet sand, distributary bay, sand bar, sand beach, shore-shallow lake of mud. From the bottom to top vertically, the strata have a complete retrograding sequences, including braided river delta plain,braided river delta, shore-shallow lake. Combination of vertical and plane distribution of sedimentary micro-facies, there are two types of the reservoir sedimentation models, namely, the model of the braided river delta and lake in the target zone.