The deterioration of silicate cultural heritage caused by the salt damage is a difficult problem for cultural heritage conservation. It is more difficult to study the relationship between rock alteration behavior due to brine solution erosion and rock microstructural change. Mineral automatic quantitative analysis (TIMA), X-ray diffraction (XRD) and X-ray fluorescence (XRF) spectrometry were carried out on sand and gravel blocks collected from the cliff of Mogao Grottoes. It was found that the sodium and potassium feldspar components in the tested rock block underwent phase alteration to kaolinite after the freeze-thaw cycle in the brine solution, with the rock block fractured. The ion exchange and substitution in brine solutions were the main causes of rock alteration in the process of freeze-thaw cycle. The alterations of calcite, dolomite and chlorite were manifested as phase dissolution and reconstruction, and quartz had partial lattice distortion. The mineral composition of conglomerate is transformed and reconstructed by the change of external environment. Moreover, the change of cliff microstructure leads to the deterioration of its mechanical properties, resulting in cliff instability and cracks, which are the main reasons for the bottom cutting and collapse of site base.