Ordos Basin is a large Mesozoic inland depressed basin with rich oil and gas resources. Triassic Yanchang Formation is the main oil-bearing formation , where a set of lacustrine-delta facies deposits is developed. The reservoir is a typical lithologic reservoir with poor reservoir conditions and high reservoir heterogeneity. The forming of the reservoir is mainly under the control of high quality of source rocks and favorable reservoir sand bodies. The late constructive diageneses and tectonisms are closely related to the improvement of the reservoir. The overpressure of Chang 7 is the main driving force for the hydrocarbon migration and accumulation. Effected by the aspects of depositional environment , reservoir features , source rocks and the combination of the reservoir and seal , NE meandering river and SW braided river delta depositional patterns are developed. The delta front subsea distributary channel and mouth bar are the most favorable sedimentary facies belt for the generation of Yanchang Formation reservoirs.