The characteristic correlation of sequence stratigraphy has indicated that there isa differentiation regulation in lateral at the top surface (the T2/T1) and the bottom surface (the T3/T2) of Middle Triassic Leikoupo Formation in lithology in northern Sichuan Basin. Therefore, two芋-order sequences are identified, in which the high-level system tract (HST) is generally absent in SQ2, the upper subsequence. Based on analysis of lithofacies palaeogeography in theⅢ-order sequence stratigraphic framework, it is shown that the environments of evaporative carbonate platform and restricted platform was dominant for a long time during the middle Triassic epoch in northern Sichuan Basin so that the underdeveloping carbonate grain textures indicate lack of mark of reefs but abundant algal mats, which results in existence ofa little algal-clastic grainstone and dolostone and fine-to medium-crystalline dolostone. A sort of slope facies breccia is recognized at Gongnong Zhen outcrop. The location of platform margin is confirmed. According to the research results of sedimentology and lithology, a typical model of Middle Triassic steep-sloped enclosed rimmed platform Facies in epicontinental sea iss recommended for the northern Sichuan Basin.