Abstract: Because of clay mineral has important effect on engineering behaviour of expansive soils,for this rea-son, the analysis of clay mineral composition has consistently ply great attention to expansive soils in home and abroad. On the basis of detailed discuss on the advance and present problems in the identification of clay mineral composition of expansive soils before end of last century, this paper presents the results of the 19 Samples quan-titative analysis on the clay mineral composition of expansive soils by new technique of quantitative analysis of XRD at the present. The samples of expensive soils collected from different region and formation type in China.The three prepared slides (normal, Heated and glycolated) of each Somple of the 19 treated Samples were X-rayed. Glycolation method can helps in the identification of the mixed layer type of clays with expandable layers,heating of the oriented clay samples to 550℃for two hours can helps in the identification of the kaolinite and smectite. The study result showed that major clay mineral in expansive clay mineral(S、I/S、K/S、C/S),especial I/S mixed-layer mineral than 80%in full clay mineral,id est expansive clay mineral content than 30%forwhole dry soil weight. Therefor,expansive clay mineral is control engineering properties of expansive soils.