In this paper, we discussed the sedimentary and diagenetic environments of the Early Triassic Yinkeng Formation at the west Pingdingshan section, Chaohu, Anhui Province, based on the detailed analyses of sedimentary sequence, mineral composition, sedimentary texture and structure, chemical components, as well as carbon and oxygen isotopes of the carbonates. The results indicate that the Yinkeng Formation contains four sedimentary facies, including the shallow open platform, upper slope, lower slope, and deep basin from bottom up, with the water depth and sea level deepening and rising, respectively. Nodular limestones, which are composed of nodules and matrix, are common in this formation. The nodule is gray or gray white micritic calcite while the matrix occurs predominantly of yellow, brown yellow, and yellow gray calcareous mudstones. Three types of nodular limestones, namely the banded nodular limestone, discontinuous nodular limestone, and random nodular limestone, are regularly distributed in the section, which may reflect original sedimentary environment from upper slope, lower slope to deep basin, respectively, with dissolution gradually increasing, and following diagenetic intensity. In addition, the δ13C values of the carbonate in the Yinkeng Formation range from -597‰ to -117‰, displaying an obvious positive excursion with the magnitude up to 480‰, which may result from the biotic recovery, burial of organic matters, sea level rising, and environmental changing.