Leshan is located in the southwest edge of the upper Yangzi platform, where the member 3 of Dengying Formation is mainly composed of dolomites. Based on the field measured sections, microscopic slice identification and scanning electron microscopy analysis, and through the study of petrological characteristics in Xianfeng section, and combined with the previous studies, the member 2 and 3 of Dengying Formation can be divided into four lithologic sections: In the member 2 of Dengying Formation, the lower part is mainly consisted of algal dolomite. The dolomicrite- aplitic dolomite also can be seen in some part of the horizon. The upper part is major consisted of dolomicrite and aplitic dolomite, and the algal dolostone can be found here occasionally. In the member 3 of Dengying Formation, the lower part is dominated consisted of algal dolomite, and the dolomicrite- aplitic dolomite can be discovered in the horizon occasionally. The upper part is mainly consisted of dolomicrite and aplitic dolomite, and the algal dolostone can be seen in some part of the horizon. Depending on the microfacies analyzing and according to the standard microfacies and carbonate platform model of Wilson (1975), it can be recognized two microfacies: Dolomitic flat and algal dolomitic flat. The order combination of two microfacies composed the tidal subface of restricted platform in member 2 and 3 of Dengying Formation in the study region. On the basis of longitudinal and transverse changes of the sedimentary facies, a sedimentary facies model of the study area is built. The evolvement of the sedimentary facies model is well controlled by regressive-transgressive-regressive-transgressive sedimentary cycle with relative sea level changes. The research provides important and basic geological data for geological research and oil and gas exploration in the study area.