Abstract: The Middle to Lower Triassic strata in the Yiliang region, Wumeng mountain area, Yunnan are divided into six third-order sequences in the light of detailed examination of six geological sections, and grain size and lithological analysis of more than 500 pieces of rock samples collected from the study area. The rock types include muddy-ferruginous siltstone, fine-grained feldspathic lithic sandtone, calcareous-muddy siltstone, fine-grained lithic sandstone, fine-grained calcareous lithic sandstone, bioclastic micritic limestone, marl, marl-glauconitic ferruginous bioclastic spararenite, micritic limestone-glauconitic micritic arenite, sparry oolitic limestone, siltymuddy micritic limestone, micritic limestone, etc. According to the texture, composition and mineral assemblage, the Middle to Lower Triassic strata in the Yiliang region should be assigned to the coastal and open carbonate platform facies deposits.