During the Suining Age of Late Jurassic, western Sichuan Province was in stable subsidence, where the tectonic movement was relatively inactive. The Suining Formation was mainly a set of fresh purple-red mudstone or shale interbedded with feldspathic fine-grained sandstone to siltites, which constituted a complete sedimentary cycle. According to the analysis of base-level cycles with different scales, the Suining Formation can be divided into one long sequence cycle, three middle sequence cycles (corresponding to the three lithologic members of the formation), and some short sequence cycles. On the basis of the rising and falling base-level phases of each middle sequence, the sedimentary facies maps of the Suining Formation has been compiled in western Sichuan Province. The maps indicated that at the Suining Age, the study area was dominated by the deposition of meandering fluvial delta system which was detached by gulfs. The relatively independent reservoir-cap associations were formed and the accumulation and hydrocarbon forming conditions were also formed. During the Suining Age, the sedimentary evolution was obviously controlled by base-level cycles, and can be inherited. During the Early Suining Age (which corresponds to the deposition of member 1 of Suining Formation), with base-level continuously rising, the sedimentation evolved from progradation to aggredation. There were some small-scale alluvial fans or zonal eroded area in front of the Longmen Mountains. At the same time, three big-scale and stable deltas were respectively developed in Fenggu, Xindu and Huilongzhen, which are located in western Sichuan. During the Middle Suining Age (corresponding to the deposition of member 2 of Suining Formation), with base-level changing from slowly rising to falling, the sedimentation evolved from aggredation to retrogradation and then to aggredation. The three deltas previously developed divided into 4-5 balancing deltas. During the Late Suining Age (corresponding to the deposition of member 3 of Suining Formation), with base-level continuously falling, the sedimentation evolved from aggredation to progradation, and the deltas was pushed to lake continuously. At the same time, the terrigenous materials supply was unbalanced, thus the development of deltas in western Sichuan changed greatly. Except for a stable delta developed in Deyang, the delta in Xindu was gradually shrinking, while in Xinjin, the sedimentary evolution was from shallow lake to a large-scale delta.