Abstract: In this paper, portland cement and the stabilizers composed of the single additive or composite additive were used to stablize the soil with higher water content. The stabilized soil was studied by means of X ray diffraction and scanning electron microscropy. The results show that the compressive strength of soil with 48% or higher water content can be increased substantially by using the stabilizer composed of 83%(Wt) portland, 14% anhydrite and 3% sodium sulphate. The sulphate admixture can promote the reaction of the active alumina of soil with Ca(OH) 2 to form more aciculate AFt(3CaO·Al 2O 3·3CaSO4·32H 2O) crystal and increase greatly the strength and water stabilizing property of stabilized soil. The main reason for the sulphate admixture to increase the strength of stabilized soil is that the additive promotes the formation of more AF t.