Abstract: The braided river sand body is a kind of important oil and gas reservoir and its internal structural features have guiding effects on oil and gas exploration. Based on the braided river outcrop survey, lithofacies analysis and architectural element analysis of the Tuositai gully in the southern margin of Junggar basin, 6 types of lithofacies are summarized，and 5 levels of bounding interfaces are divided，and 5 types of 4-level architectural structural units are identified including stable flow channel, high flow regime channel, sand bar, abandoned channel filling and floodplain, which are characterized by the lithofacies assemblages of St-Spx-Sp-Sr, St-St-St, St-Spx-St-Sr, St-Sr-Fl and Sr-Fl-M, respectively. According to the characteristics of each structural unit and its bounding surface, 4 types of muddy interlayer such as mud in floodplain, interchannel mud, mud within sand bar and mud in cross-bedding layer are identified. The study results show that the target stratum is a typical sandy braided river deposit characterized by multiple periods and cycles with coarse grain in the lower and fine grain in the upper and gradually decreased flow energy. In the braided river sand body, the St and Sp lithofacies are the most stable, which are the basic elements of dominant reservoir units. The high flow channel and sand bar are favorable reservoir structural units. The sand bodies formed by these two types of structural units are featured with large thickness, good lateral continuity and weak heterogeneity, which are conducive to oil and gas accumulation and can be the most favorable intervals in braided river reservoirs