Abstract: Through in?depth analyses of the lithostratigraphy, biostratigraphy, logging stratigraphy and carbon and oxygen isotopes of the Ordovician from new wells in the Maigaiti slope, the Lianglitage formation of the Upper Ordovician in this area was confirmed to be unconformity contact with underlying Yingshan formation of the Middle?Lower Ordovician and overlying Yimugantawu formation of the Lower Silurian. The Lianglitage formation is dominated by grey, yellow?gray, brown?gray micrite, sand?cutting micrite, sparry grain limestone with thickness of90~140m, intercalated with a little purple calcareous mudstone, in which conodont biozone ofYaoxianognathus neimengguen sisoccurred and theδ13C in coring section ranges from0.3‰to0.9‰. Compared with the sections of Tazhong (down hole)?Bachu outcrop area, the Lianglitage formation lacks the lower part (4~5members). There existed three suits of favorable reservoir?cap rocks assemblages developed in the Ordovician strata in Maigaiti slope: a set of most favorable reservoir (Yingshan weathering crust karst?like grain limestone)cap rock (Lianglitage micrite) assemblage; a good reservoir (Lianglitage reef flats)?cap rock(Lianglitage reef cover micrite or Sangtamu mudstone assemblage; a favorable reservoir (Lianglitage grain limestone)?cap rock (Lower Silurian mudstone) assemblage