Abstract: Ningming county in Guangxi is famous for wide distribution of expansive soil.In the 1970s,lots of industrial and civil buildings were seriously damaged due to Ningming expansive soils.Therefore a detailed site investigation and deforemation monitoring as well as systematic theoretical researches on the expansive soils were carried out by many experts and scholars at that time.Since the beginning of the new century,the construction speed of expressway increased quickly,many expressways traverse through expansive soil regions,such as Nanning to you yi-guan expressway.Because of the special hazard features of expansive soils and the high quality standards of expressway contruction,the comprehensive study of the geotechnical properties of Ningming expansive soils and their influence on the construction and operation of expressway provided with important theoretical meaning and engineering value.On the other hand,with the progress in quantitative testing technology for the identification of clay mineral and the development in the basic theorefical researches on expansive soils in recent 20 years,this study made great progreses with the understanding of Ningming expansive clay minerals,the relationship between the engineering properties of expansive soils and their cause of formation,the drying and reactive action and the effect of the expansive soil improvement.