Abstract: The origins of Chang-6 reservoir horizons in Wangyao district of Ansai oilfield are interp reted to be a river-dom inated delta deposited in lacustrine environm ent.The main sedimentary microfacies of Chang-6 reservoir horizons in Wangyao district include distributary channel,distribu tary mouthbar,front sand sheet and in terdist ributary deposits.The distributary channel fills to show a finning upward sequence.The distributary mouthbar deposits consist of overall coarsing upward sequence and other homogeneous sequences.The distributary channel and distributary mouthbar sands coalesce to constitute the dominated petroleum reservoirs.Prog radation of two distributa ries constructed at first only a delta skeleton in the Chang-6₁² sand layer.Rapid sed imentation during the period of Chang-6₁¹ lead to rapid progradation basinward of multiple distributa ries.The deltaic microfacies are interpreted and delineated based on depositional sequence and sandbody geometry.Sandbody microfacies are the main factors affecting movement of oil and water.Comprehen sive descriptions of sedimentary microfacies are good methods to predict reservoir performance.