Abstract: In the light the provenance and seismic analysis, two depositonal systems are recognized for the Middle Jurassic Shaximiao Formation in the central part of western Sichuan depression, including the alluvial fan-alluvial plain (braided stream) -braided delta-lake depositonal system controlled by the Longmenshan provenance in the western part, and alluvial plain (meandering stream) -meandering delta-lake depositonal system controlled by the Micangshan-Dabashan provenance in the eastern part. The oil and gas accumulations reside mostly in the meandering stream-meandering delta depositonal system in the eastern part. Our knowledge of the depositonal systems in this study may be helpful to the future exploration and development of the oil and gas resources in the study area.