The Mianyang-Lezhi-Longchang-Changning intracratonic sag was formed by the Xingkai taphrogenesis during Early Cambrian.Based on the contrastive researches on the Sinian reservoirs across the intracratonic sag from southwest to northeast,it is concluded that the intracratonic sag has a significant influence on the weathering crust karst,burial dissolution and hydrothermal action as well as the reservoir quality in Dengying Formation.Being adjacent to the intracratonic sag,there develop more intensive weathering crust karsts with corrosive vugs and caves,the bitumen content of the reservoir is high,the organic acid burial dissolution and hydrothermal action is stronger,porosity and permeability are bigger and the reservoir quality is better.Due to the existence of faults and fractures on the east margin of the intracratonic sag,the burial dissolution,the siliceous hydrothermal action and the hydrothermal dissolution are more intensive than that on the west margin.