Abstract: Clay minerals occur extensively in various geologic enviro nments. In g eotechnical engineering aproblem is always involved about the precaution again st natural calamities and the treatment of soft ground. The key of the problem is controlling and reducing the content of water in clays, and transforming clay minerals from hydrophilic into hydrophobic. In this way the clays won't adsorb w ater an d swell as they were in contact with water, and thus the soil stability could be m aintained. We call the modification of clays for retaining the soil stability in geotechnical engineering ‘passivation’. As the surface of clay minerals inter acts with passivators during the process of passivation, the surface structure of cl a y minerals will be changed and the hydrophobility of clay minerals increased, th us the mechanical strength of clay mineral in the whole will be raised. The surf actant is a very important component in the passivator. However, the adsorption o f surfactants at the interface between solid and liquid is controlled not only b y the properties of surfactants, but also by the properties of solids, pH of sol utions and temperatures etc. So research about the surface structure and the pr operties of solids and the interaction of clay minerals with passivators is an i mport ant way to increase the passivation effect. 　　Physical and chemical study of mineral surface is an extremely active frontier f ield of scientific research. Our study is based on the physics-chemistry of min e ral surface, and involves many analytical methods: XRD, IR, Raman, MAS NMR, SEM, TEM, AFM, and the parameter measurement of solid mechanics and engineering mec hanics. This paper systematically investigates the change of surface structu re and properties of clay minerals (kaolinite, illite and montmorillonite) befor e and after passivation. In order to clarify the mechanism of clay mineral passi vation and to provide theoretical basis for the clay stabilization in resolving various engineering and calamity problems, analyses and preparation work of pass ivators of clay minerals have been done. The work combines the basic research of mineralogy with the experimental investigation of geotechnical engineering.