Abstract: Regarding the complicated sedimentary system of alluvial fans located in the margin of Junggar basin, with the data of well patterns and outcrops and using the method of hierarchical bounding surface analysis, the paper performs a leveled dissection on the internal architecture of alluvial fan reservoirs and establishes the reservoir architecture patterns and 3D geologic models for alluvial fans of the lower Karamay formation in the Wellblock Hong-18 of the northwestern margin of the basin. The 4-order architecture of the alluvial-fan sedimentary system is made up of trench-flow sandy conglomerate, laminar-flow gravel, high-energy channel sandbody, low-energy channel sandbody and runoff channel sandbody, meanwhile, it includes some low-quality reservoirs such as flood sandbody, sheet-flood sandbody and fine-grained flood deposit. The internal architectures of different facies belts in the alluvial fans are different. Trench flow-laminar flow facies belts are dominated by connected sheet sandy conglomerate which is the product of the superimposition of complicated sandy conglomerate and a single sandy conglomerate body is 1.2~1.6 km wide; the braided-flow facies belt is the complex superposition of the high-energy channel sandbody, low-energy channel sandbody and sheet-flood sandbody, among which the high-energy channel is 400~600 m wide and the low-energy channel is 100~250 m wide; the runoff channel belt is distributed in the fine overbank deposits in the shape of mosaics and shows an isolated narrow strip shape, and the width of a single runoff channel ranges from 50 m to 80 m. Based on the detailed geological research, the paper establishes 3D architecture models for the study area by using deterministic modeling combined with artificial interactive methods