Abstract: Mahu depression is the most hydrocarbon abundant depression in Junggar Basin. The slope zone of the depression is located in the advantageous oil and gas migration area with development of large-scale Triassic paleo-anticline and nose structure. It has the favorable structural conditions for hydrocarbon accumulations on a large scale. Hydrocarbon migrates along the unconformity surface between Triassic and Permian and accumulated in the nose uplift zone. The Triassic Baikouquan Formation is shallowly buried, where the fan delta frontal favorable facies zone developed. The slope zone has the geological conditions of reservoir, sealing, and conducting for large-scale hydrocarbon accumulations. Guided by the pattern of fan-controlled large-area accumulation and based on the study of the main factors controlling accumulations, it is found that the fan delta frontal facies zone controlled the physical properties and oil bearing properties of reservoirs while the facies zone and material source controlled oil and gas abundance and high yield. A number of blocks with effective and quality reserves were found on the basis of re-identifi cation of the neighboring fan bodies. Exploration practice indicates that the Triassic Baikouquan Formation in the slope zone of Mahu depression is characterized as fan-controlled large-area accumulation and becomes a new base to increase oil and gas reserves and production for PetroChina^’s Xinjiang oilfi eld.