Through the research on sedimentary strata of Nanhuan Period-Early Paleozoic of Back-Longmenshan tectonic belt in the northwest margin of Yangtze Block with the methods of petrology and sedimentary strata, the sedimentary and forming environments of Nanhuan Period-Early Paleozoic of Back-Longmenshan tectonic belt were discussed. The results indicated that the sedimentary environments of Nanhuan Period-Early Paleozoic of Back-Longmenshan tectonic belt could be divided into two stages, including the division-stable stage of Nanhuan-Sinian Period and the extension and division-collapse stage of Early Paleozoic; Back-Longmenshan tectonic belt had the repetitive process of divergence→lifting→partial divergence→lifting→divergence during the extension and division-collapse stage of Early Paleozoic; aulacogen sedimentary in Maoxian Group of Silurian System.