Abstract: Neogene hard clays composed of Aeolian hipparion clay and palaeo Sanmen Lake fluvial deposit clay in Baoji City area of Shaanxi province constitute typical hard clay formation in the southern part of China's loess plateau and also make up the sensitive and key controlling strata in the development of large-scale deep-seated loess slides along the slope of the Loess Yuan on the northern bank of the Weihe River. In order to recognize this type of special sedimentary material, especially the swelling clay mineral (montmorillonite and its mixed layer mineral), the authors collected more than 30 samples according to the spatial distribution features of the clay strata, and then analyzed macroscopic and microscopic structural characteristics. Pipette method, fine X-ray diffraction (XRD) technology, and glycol ether polar organic molecular adsorption method were used to conduct a quantitative analysis of sample granulometric composition and high accurate determination of clay mineral composition. In addition, a brief analysis of expansive characteristics and slope failure relationship between Neogene hard clays was carried out in combination with landslide distribution and slope failure features.