The Yan 9 Reservoir of Yanwu Area was one of the important oil-bearing formations of Yan’an Formation in Ordos Basin, the research degree on the sedimentary facies of the sedimentary facies was lower. Combined with the structure and sedimentary evolution characteristics of the whole Ordos Basin, by synthetically using the geological theories, such as petrology, sedimentology, log-ging geology, sequence stratigraphy and so on, and through researching in detail the mudstone color, petrological characteristics, sedimentary structural characteristics, paleontologic evidence and logging facies markers, the result showed that Yan 9 Reservoir of Yanwu Area belonged to a braided river delta sedimentary system, where developed braided river delta plain facies. It is further divided into 4 sedimentary microfacies, i.e. the distributary channel, the inter-flow de-pression, the natural levee, and the swamp. According to the distribution and evolution of sedi-mentary microfacies in the Yan 9 Reservoir, and combined with regional sedimentary and tectonic background, the sedimentary mode of the Yan 9 Reservoir is established in the study area.