Abstract: Based on classic sequence stratigraphy theory,in combination with high-resolution base-level cycle analysis,according to drilling,seismic,paleontology,electric logging curve data,the sequence stratigraphy research of Dongying formation,western subsag in Bozhong sag has been carried out.Dongying formation can be divided into three sequences,namely Dong-first,Dong-second and Dongthird sequences,among them,Dong-second sequence is better developed and can be further divided into lowstand system tract,lake expand system tract and highstand system tract.Finally the sedimentary system type of each unit has been recognized,and the lithofacies palaeogeography has been restored.The sedimentary system of western sub-sag in Bozhong sag and the surrounding area is mainly controlled by provenance systems comes Shijiutuo and Shaleitian uplifts.According to the development time of sequence and system tract,the plane distribution rule and vertical evolution rule of sedimentary system in Dongying formation have been analyzed.