Abstract: The tectonic environment of Mahu sag in Junggar basin was relatively stable in Badaowan stage of Early Jurassic, during which grooves and slopes were developed and the sediment supply was sufficient, providing conditions for development of braided rive delta. The sediments of the braided river delta that are characterized by coarse grain, low maturity, developed tractive-current depositional structure, incision and superimposition of multi-stage underwater distributary channel vertically and normal cycle of sedimentary sequence and so on, can be divided into 2 subfacies such as braided-river delta plain and braided-river delta front. On the plane, different slope gradients in different areas result in the differences of sizes of braided river deltas whose sizes are relatively large in steep slopes and relative small in gentle slopes. Vertically, different subfacies associations and sandbody configuration were developed at different stages of lake level rising. Braided-river delta plain was mainly found at the early stage of lake level rising; braided-river delta front was the dominant subfacies at the middle stage of lake level rising; mud-coated sand type of braided-river delta front was developed at the late stage of lake level rising.