Abstract: On the basis of analyses of the characteristics of the cumulative probability curve of particle size and of the depositional characteristics(including lithology,fabrics and paleontology),the sandstone bodies of Lower Cretaceous in west Jiuquan basin are divided into 13 genetic types in five depositional systems:the diluvial fan deposits,thc fluviatile deposits,the deltaic deposits,the littoral deposits and the turbidites.Differcnces of sandstone bodies deposited under varying environments are described.study of the evolution of the sedimentary facies in early Cretaceous in the basin suggests that it underwent expansion and contraction of the water body twice during the period,resulting in the widespread water encroachment in the early part and the reduced scope of encroachment in the later part.The former was favourable for oil generation and the latter for sandstone reservoir formation.