Many oil reservoirs that relate to Carboniferous volcanic weathering crust have been discovered in Junggar Basin.Taking Carboniferous volcanic rocks in Chepaizi area in the western margin of the basin as an example，the development of weathering crust is analyzed by geological，geochemical and well logging techniques，and the hydrocarbon accumulation in Carboniferous formations is clarified. Studies show that the volcanic weathering crust at the top of Carboniferous volcanic rocks in Chepaizi area consists three layers，including clay layer，hydrolyzed layer，and leaching layer. The weathering time determines the thickness of the weathering crust，the palaeography controls the integrity of structural layers，and the lithology and fault affect the local variation of the weathering crust. The petroleum geologic significance of weathering crust on hydrocarbon accumulation mainly includes：①Various volcanic rocks in the leaching layer can form favorable reservoirs；②Clay layer and hydrolyzed layer are effective caps for weathering crust stratigraphic traps；③Leaching layer and overlying carpet sand are important transverse transport layers for hydrocarbon migration. Controlled by the weathering crust structure，there are 3 kinds of transport modes in the Carboniferous volcanic weathering crust，including fault and carpet sand transport mode，fault and leaching layer transport mode，and carpet sand and hydrolyzed layer transport mode. The oil of Carboniferous volcanic weathering crust in the study area distributes in three zones，including fault-bonding zone between carpet sand and leaching layer，near fault zone，and overlap zone between carpet sand-sand leaching layer.