Many exploration wells in the southern margin of Junggar Basin have obtained high-production oil and gas flow from the Lower Cretaceous Qingshuihe Formation in wells,which proves that high-quality reservoirs is developed in Qingshuihe Formation.Based on the paleo-geomorphologic data,this paper analyzes the differences in sedimentary facies of the bottom sand body of Qingshuihe Formation,the reasons for the stable distribution of sand bodies,and the distribution patterns of different rock types,by combining analysis of the sand body structures,petrologic characteristics,heavy mineral assemblages and paleocurrent characteristics of the reservoir.The study suggests that before the deposition of Qingshuihe Formation,the paleo-geomorphology of the southern margin in Junggar Basin was characterized by the development of a steep-slope area in the south and a large gentle-slope area in the north,whereas two slope breaks were globally developed in the gentle-slope area.During the depositional period of Qingshuihe Formation,the study area was in the process of lake transgression,and retrogradational braided-river deltas and fan deltas were formed under the control of paleo-geomorphology.In the southern steep-slope area,fan deltas depositional system was developed,and the thickness of sandstone and conglomerate reservoirs is at the range of 10-30 m.In the northern gentle-slope area,three stages of regressive braided-river deltas depositional system were developed under the control of two slope breaks,resulting in the widely developed sandstone reservoirs in the middle and northeastern parts of the southern margin in Junggar Basin.The sandstone reservoir formed by northern and northeastern source system with a thickness of 20-50 m and relatively good physical properties,making it a favorable reservoir development area for the Qingshuihe Formation.