|Abstract:On the basis of summarizing and analyzing the theory of gravity flow sedimentation, the sedimentary characteristics and sedimentary model of the Chang 7 Member of Yanchang Formation in Longdong area of Ordos Basin are systematically studied by using a large number of core, outcrop profile observation and logging data. It is considered that sandy debris flow and turbidity current deposits are mainly developed in Chang 7 Member of Longdong, and slip and slump rocks are locally developed. Affected by multiple sources, lake basin bottom shape and lake shoreline migration, the sedimentary sand bodies in the study area do not show obvious fan-shaped. Sandbodies in Jingchuan-Huachi area controlled by steep and narrow slopes in southwest China distribute in strips, and channel-type gravity flow deposits are developed, and sedimentary microfacies is divided into six types: restricted channel, unconfined channel, flank overflow, inter-channel, leading edge lobate sand and deep lake mud. At the bottom of the lake basin, Qingcheng-Huachi waterway intersects and overlaps, forming a large area of connected sand bodies. In Ningxian-Heshui area controlled by Southern provenances, due to relatively gentle slope gradient and abundant provenance supply, a slope sedimentation model dominated by slump structure is formed. According to the slip distance, it can be divided into two subfacies: near-source sedimentation and far-source sedimentation. The sedimentary microfacies can be divided into four types: irregular slumping, sandy debris flow tongue, lobate turbidite and deep lake mud. In the southern part of the study area, sandy debris flow tongue is the main body, and the tongue body overlaps vertically and horizontally in many stages on the slope, forming a large area of continuous sand body of thin and thick sand Interbedding. Through the establishment of sedimentary model and identification and division of sedimentary microfacies of Chang 7 Member in Longdong, it provides important guidance for fine characterization of sand body distribution in the study area, and also provides basis for scale production of tight oil horizontal wells in the area.