There is good potential for petroleum exploration about Oligocene—Miocene Series in the Ganchaigou—Xianshuiquan area, Qaidam Basin, but there are still no breakthrough. Why? The poor effort to characteristics and regularity of the sedimentary facies distribution in this area is one of the main causality. In this paper, based systematic analysis of the facies marks, such as types and colors of rocks, sedimentary structures, ancient creature etc, the types and their characteristics of the sedimentary facies, such as alluvial fan, fanshaped delta, lacustrine and sublacustrine fan were identified on the basis of regional geological background, field geological section plane, core analysis etc, and the sedimentary facies distributional characteristics and regularity were revealed and the depositional pattern was builded up by established the distribution diagram about single well, cross section and plane sedimentary facies. The results showed that the main beneficial target for the next petroleum exploration was mainly in connection with all kinds of microfacies sands, such as beach, bar and channel within alluvial fan, fanshaped delta, lacustrine and sublacustrine fan in the Ganchaigou—Xianshuiquan area, Qaidam Basin.