Abstract: The outcrop development characteristics of lower Jurassic on the periphery of the Wudun sag in Dunhuang basin are of great significance for the analysis of the material source system and the division of sedimentary facies. The measurements of the field outcrop show that the outcrops of Jurassic are alluvial fan, fan delta, sublacustrine fan, shallow to semi-deep lacustrine facies sediments under the influence of tectonic conditions,paleoclimate and source, mainly exposed fan delta facies,sub-lacustrine fan facies deposition, the granularity of the sediment changes rapidly in vertical direction. In the early Jurassic, the sedimentation of the Dashankou formation was controlled by the boundary fault of Sanwei mountain. In the early stage, the alluvial fan-fan delta was deposited, and the deposition rate was fast. In the middle and late stage, the lake plane continued to rise, and the sediment particle became fine, and the fan-deltaiclacustrine facies developed. Sanwei mountain extruded and uplifted in the late Yanshan and strike-slip extrusion in the Xishan stage, causing the alluvial fan and fan-delta plain facies of the Dashankou formation to surface. The wedge-like sand or the turbidite sandstone reservoir and the semi-deep lake facies hydrocarbon source rock of the front of the fan delta in the sag belt of the Wudun sag are vertical stacking and transverse superimposition, they are the potential oil-gas-rich regions and have great exploration potential.