Based on the analysis of regional tectonic background,the understanding of tectonic-sedimentary characteristics and sedimentary facies evolution of Leikoupo Formation in northwestern Sichuan Basin has been deepened through drilling core observation,outcrop profile investigation,thin section identification,outcrop-well profile correlation and typical seismic profile interpretation.The results show that:(1)The uplift of the Xuefengshan ancient land during the Leikoupo period of the Middle Triassic intensified the geographical background of"low west,high east"in the Upper Yangtze sea.With the continuous uplifting of the Luzhou palaeohigh and Kaijiang palaeohigh,the subsidence center and depocenter during the Leikoupo period was formed in Jiangyou-Mianzhu area of northwestern Sichuan Basin,and in Late Triassic the depression extended southward to the Kuahongdong area of Emei County.(2)Controlled by the geographical background and sea level change,three major sedimentary facies,i.e.,platform margin facies,limited platform facies,and evaporite platform facies,are developed from west to east in Leikoupo Formation.Shoal subfacies is developed in the platform margin facies,which mainly consists of sandy shoal and oolitic shoal microfacies.The limited platform facies consists of shoal,tidal flat and lagoon subfacies,including sandy shoal,algae limestone flat,calcareous dolomite flat,tidal channel,desalinated lagoon,saline lagoon,brackish lagoon,and other microfacies.The evaporite platform facies is composed of evaporite flat and salt lake subfacies,with microfacies of gypsum flat,gypsum-dolomite flat,dolomite-gypsum flat,dolomite flat,gypsum-salt lake and halite lake developed in them.(3)The platform margin shoal has a significant scale with densely packed internal clastic and oolitic grains.Conversely,the internal shoal has a smaller scale primarily characterized by algae debris particles.We propose a sedimentary model of"platform margin facies-limited platform facies-evaporite platform facies"in the Leikoupo Formation,and the sedimentary changes are controlled by the sedimentary base tilting northwest and the transgression-regression cycle of the sea level.