Abstract:The Jurassic Shuixigou Group in the LowerMiddle western segment of the southern margin of the Ili basin is divided into four depositional systems based on field geological observations of outcrops and borehole cores and statistic analysis of plenty of borehole core records and logging interpretation data. The four depositional systems are the alluvial fan depositi Onal system of the Lower Jurassic Badaowan Formation, braided delta depositional system of the Lower Jurassic Sangonghe Formation and Middle Jurassic Lower Xishanyao Formation, shallow lacustrine and swampy depositional system of the Middle Jurassic Middle Xishanyao Formation and meandering river depositional system of the Middle Jurassic Upper Xishanyao Formation. The sed Imentary facies characteristics of each depositional system of the Shuixigou Group in western segment of the southern margin of the Ili basin are discussed in detail and the relationship between the formation of uranium deposits and the depositional Sandstonetype system and sedimentary facies of the Shuixigou Group is studied. The braided delta depositional system is the MOS T favorable one for the formation of uranium deposits whereas Sandstonetype; the distributary mouth bar and sheet sand subfacies of the delta front facies, the braided stream subfacies and the distributary channel subfacies of the delta plain facies and the and distal fan subfacies of Midfan the alluvial fan facies are the major sedimentary facies for sandsto Orecontrolling Netype uranium deposits.