Abstract: Qian-5 member of upper palaeozoic Shiqianfeng formation in Yanchang block is of great natural gas exploration potential,in order to identify the depositional environmental characteristics and sedimentary evolution regularity,based on large quantities of drilling,logging and core test data,typical sedimentary facies markers were identified,and therefore,the sedimentary micro-facies types and characteristics were analyzed,and then the plane distribution of sedimentary micro-facies was finally clarified.Research results indicated braided river delta sedimentary system was mainly developed in Yanchang block,taking JingbianHengshan-Zizhou-Wubu as a boundary,braided river delta plain subfacies in northern area and braided river delta front subfacies in southern area.The underwater distributary channels changed frequently,laterally moving back and forth and vertically,superimposed with several phases,and then massive sandstone sedimentary bodies were formed,which was considered to be the optimum reservoir rock in Yanchang block.