Abstract: The hydrocarbon accumulation conditions and exploration potential of the Carboniferous?Permian in Mahu sag and its periphery in northwestern Junggar basin have received little research attention due to deep burial depth and associated low exploration degree. This paper analyzes the basic hydrocarbon accumulation conditions and indicates there exist three source sequences in this area, including the Carboniferous, the Jiamuhe formation and the Fengcheng formation of the Lower Permian, which are all in highly matured evolution stage, with sufficient oil?gas source, and dominated by highly matured hydrocarbons. In this study area, large structural and stratigraphic traps are developed widely, including inherited foreland uplift anticlines, piedmont anticlines, fault block traps, stratigraphic and fault?stratigraphic traps. It is found in deep Mahu sag that special types of reservoirs are developed, such as volcanic reservoirs of the Carboniferous and the Jiamuhe formation and the dolomitic reservoir of the Lower Permian Fengcheng formation. In addition, wide development of fault, fracture and weathering crust has resulted in improvement of the reservoirs quality. It is suggested that the deep?buried lower hydrocarbon accumulation assemblage has the basic geological conditions for forming oil and gas pools with relatively large scale and high production, and could be as a new domain for petroleum exploration in Junggar basin. Also, the anticline surrounding Well DA?1 has been selected as preferred exploration target to look forward to get breakthrough