Abstract:he Ediacaran Dengying Formation in the Upper Yangtze area not only recorded the co- evolution of environment and life at the end of the Precambrian, but the massively developed mound- shoal deposits are currently becoming an important target for oil and gas exploration in deep ancient carbonate rocks in the Sichuan basin. Therefore, analyzing the evolution of the Dengying Formation sedimentary environment can not only constrain the global sea level change and the evolution of the paleo- ocean environment in the late Ediacaran, but also has important value for deep oil and gas exploration in the Sichuan basin. Previous studies lack detailed description and explanation of the sedimentary environment evolution and relative sea level changes of the Dengying Formation at the end of the Ediacaran in the Upper Yangtze area, which severely limited the progress of the above studies. Based on detailed field sedimentology and microfacies analysis and interpretation of Dengying Formation in Qingping section of Mianzhu in the northwestern margin of the Upper Yangtze, 21 types of rock microfacies were identified, mainly composed of granular and microbial dolomites. According to the analysis of microfacies assemblage relationship, it is considered that there are several shallower subtidal- intertidal- supratactic sedimentary sequences and meter- level sedimentary cycles composed of several grain banks and microbe mounds. On this basis, the sedimentary environment evolution and sea level change process of four transgression- regressive secondary cycles and two exposed erosions are described in detail. The sedimentary model of shallow water carbonate platform in the Mianzhu area in the western margin of Yangtze Platform in Late Ediacaran is established, which is characterized by tidal flat facies, microbial mound bank body and grain bank. Based on the characteristics of sedimentary microfacies, combination of microfacies and vertical evolution of sedimentary facies, it is believed that the evolution of the sedimentary environment in this area is mainly affected by secondary sea level fluctuations, and the middle and upper part of the transgression- regression secondary cycle may be high- quality reservoirs in the Dengying Formation. The two exposure unconformities in the main development horizon may be closely related to the sea level drops caused by ice age events.