The high-resolution seguence stratigraphy of the Jurassic System in west Junggar Basin was studied and six unconformity surfaces (or sequence boundaries) were recognized-The Jurassic System could be divided into five sequences according to the surfaces

and an isochronic formation skeleton was set up which coincides with Junggar Basin. The long-term base level rising cycle of sequence-I is composed of braided river alluvial fan; the long-term base level falling cycle of sequen-1 consists of shore-shallow lake→delta front→delta plain . The long-term base-level rising cycle of sequence-2 is composed of basal braided channel sandstone-conglomerate→meandering stream→delta; its falling semi-cycle mainly consists of shore-shallow lake→delta front. The long-term base-level rising semicycle of sequence-3 is composed of braided river→meandering stream→delta; its falling semi-cycle consists of shore-hallow lake→deta front.