Abstract: Sand grain mucky soil is a special type of lacustrine sedimentary soft soil in the Dongting Lake area with a modest layer of fine silty sand. Analysis of the microstructure changes in the soil during consolidation can explain the engineering phenomenon on a macro level, and sheds light on the nature of soil deformation. In this study, X ray diffraction test and scanning electron microscope test are conducted to observe the mineral compositions and the microstructure of the sand grain mucky soil, and the change in microstructure parameters of the sand grain mucky soil during consolidation. The results show that (a) the sand grain mucky soil is primarily composed of chlorite, muscovite and quartz, and its microstructure is flake and tabular; (b) as the consolidation pressure increases, the increasing rate of the equivalent particle size is higher in the early stage than that in the later stage, and the morphological parameter of structural units increases first, and decreases later; and (c) there is negative correlation between the compressibility and probability entropy of structural units of the sand grain mucky soil.