The sliding zone soil of Motuo and GelinLandslides were tested with X-ray diffraction, X-ray fluorescence, and infrared absorption spectra. Its compositins of main minerals and clay minerals, even the chemical compositions were comprehensively analyzed. The results show that the composition of the main minerals was controlled by alluvial fan composition, and the contents of clay minerals accounted for 9% and 10% respectively, with a large number of illitecontained in the sliding zone soilofMotuoLandslide, which reflects that the landslide had a high slip rate. There were no exotic corbonates minerals or secondary clay minerals contained corrosive substance with poor mechanical properties filled into theslidingplane because of the closed system, based on the infrared absorption spectrum with no peaks arising from CO2-3, HCO1-3 or C—H, as a positive affect result of the stability of these lamdsiles.The samples of sliding zone soil contain a certain amount of halloysite, reflecting that the landslides in the area of Motuo developed in a very humid and warm environment. With Na2O and CaO preserved in the closed system, a large number of illite/montmorillonite mixed layer formed in the sliding zone soilofGelinlandslide due to the strong water-rock interaction in thesliding plane with the decomposition of illite. The frictional strength of sliding zone was largely reduced due to the clay mineral assemblages, leading to the activity risk of landslide increasing.