The Pengyang oilfield, next to the Xiyuan Thrust-belt of Ordos basin, is located in the southwest part of Tianhuan depression with a key target of the seventh, eighth and ninth member of Jurassic Yan’an Formation. Structure of the Yan’an Formation shows a complex NE-SW striking syncline with a saddle in the middle. The Yan’an Formation, unconformbly overlying the Triassic Yanchang Formation toward southwest, was deposited as sandy braided-river sediment under humid conditions with sandbodies having good lateral continuity, porosity and permeability. The Yan’an Formation reservoirs mainly sourced from carbonaceous mudstones and oil shales of the sixth and seventh member of Yanchang Formation. The source rock became mature since the late Jurassic and approached a climax of hydrocarbon generation during the late Cretaceous. It provided petroleum to the reservoirs by faults, fractures and the unconformity on top of the Yanchang Formation. Structure is the most important control on hydrocarbon accumulation of the Yan’an Formation sandstone reservoirs, followed by sandbody distribution and hydrocarbon preservation conditions. These three controls resulted in structural, structural-lithologic and stratigraphic overlap reservoirs. The northern and the eastern part of the studied area have better hydrocarbon preservation conditions than the other parts, in which low-amplitude anticline and nose are the most favorable areas for hydrocarbon accumulation in the Yan’an Formation.