Abstract:Through study on outcrops, lithology, logging features in the studying area, upper and lower parts of Neogene Youshashan formtion in Chaidamu basin have been divided into five important types of sedimentary facies, including alluvial fan facies, fluvial facies, fan delta facies, delta facies and lacustrine facies, and have been described in detail. By using multifactor comprehensive mapping method based on single factor, plane distribution map of sedimentary facies of Youshashan formation has been made. Sedimentary facies zone is the basic factor for controlling reservoir distribution and characteristics. Combining with sedimentary facies belt graph, reservoir facies belt in Youshanshan formtion have been circled. Favorable reservoir facies are mainly composed of delta front sandstone, alluvial fanfan delta distributary sandstone, channel shallow lake beach and daml. They mainly distributed in Shaxi, Wunan, Xianshuiquan, Yueyashan, Honggouzi and Aerjin slope belts. While reservoir facies poorly developed in Jianshan area.