Abstract: The Sinian System exposed in the Southern Yardang Mountains, Xinjiang, is complete. It has a clear stratigraphie sequence with a total thickness of 2017.0m It overlies unconformably the pre-Sinian and underlain diseonformably the Cambrian. According to the lithology, it may be divided in descending order into the Hangelchaok Formation, Shuiquan Formation, Yudengou Formation, Tereeken Formation, Huangyanggnu Formation, Altungou Formation and Jianyixi Formation. The Jianyixi Formation is represented by volcanic rocks with an isotopic age of 814±97 Ma. The Altungou and Hangelchaok Formations are marked by tillite.