Abstract: Based on core description, electric logging, mud logging, core analysis data, seismic survey, etc., the sedimentary facies types and characteristics of early Cretaceous Tenggeer Formation, Baiyinchagan Sag, were studied in detail, as well as their distribution pattern. The research shows that fan delta, braided delta, lacustrine facies and turbidity fans were developped in this formation, of which the fan delta is located along the steep northern border and the braided delta found along the gentle southern slope. In addition, from the margin to the depocenter of Baiyinchagan Sag, the sedimentary environment gradually changed from fan delta or braided delta to semi-deep and deep lakes, and on the flank of fan delta or braided delta, the shore and shallow sediments were deposited. The turbidity fans are distributed in the delta front zone, pro-delta and semi-deep and deep lacustrine zones. Generally speaking, the sedimentary facies are different from the east to the west of Baiyinchagan Sag and were differentiated between the southern and the northern parts, which was controlled by the neighboring faults and the basin palaeotopography. Based on the analysis of sandstone detrital components and heavy minerals, the sediments of Tenggeer Formation in Baiyinchagan Sag came from the Bayinbaolige swell and Saihuduge salient, with the characteristics of multiphase,spasm and closing to the source rocks. The results also illustrate that the source rocks were mainly the sedimentary, and in lesser amount the igneous, with little contribution of the metamorphics.