Glauconite is closely linked to some particular sedimentary environments and conditions. Authigenic glauconite grains were discovered in micritic limestones of 3rd Member of the Late Carboniferous-Early Permian Amushan Formation in Xi Ujimqin Banner, Inner Mongolia. Through analyzing the sedimentary environment of Amushan Formation, the authors have found that the glauconite grains commonly occur as colloids around calcite cement and assume granular structure, which are indicative of typical authigenic feature, suggesting that the glauconite grains were less influenced by later diagenesis. There are framboidal pyrites around glauconite grains, implying that the sedimentary environment of glauconite grains in Amushan Formation was probably weakly reductive. The spectral curve of glauconite in limestone of Amushan Formation demonstrates typical glauconite composition characteristics. The EPMA data indicate that they are highly mature in nature. Through a comparative study of EPMA data of glauconite samples collected from different areas and different environments (such as Cambrian glauconitic limestone in Texas of the USA, glauconitic sandstone of the Late Proterozoic Qingbaikou System in Western Hills of Beijing, authigenic glauconite grains form Cretaceous sandstone in Jixi basin of Heilongjiang, and authigenic glauconite grains from micritic limestones in Late Carboniferous-Early Permian Amushan Formation of west Ujimqin, Inner Mongolia), an ideal glauconite sedimentary environment model has been established in this paper, which shows that the authigenic glauconite grains in Amushan Formation might have benefited from the semi-closed reductive microenvironment produced by the biological clastic rock at the top of the open clastic platform and the glauconitization probably occurred in the normal shallow water of slight reduction with low-oxygen levels in the air. The sedimentary environment of the low clastic rock and upper limestone of Amushan Formation in this area was characterized by two transgressions and two regressions. The formation of glauconite in Amushan Formation may represent the beginning of the transgression. The discovery and study of glauconite in this area have an important significance in such research fields as regional correlation, tectonic evolutionary framework and regional tectonic environmental analysis.