Abstract: Calcium hydroxide (CH), produced by cement hydration after cement mixed with soft soil, may be absorbed by soil and lead to the concentration of CH in the stabilized soils, which may not be saturated, resulting in reduction of the amount of Ca²⁺ and OH^- , composing calcium silicate hydrate (C-S-H). As a result, the amount of C-S-H may be decreased and the increase of strength of the stabilized soils may be prevented. In the research, some chemical reagents are used as the admixtures of cement stabilized soils, which can theoretically improve the degree of saturation of CH. The influence of admixtures on improving the strength of the stabilized soils is discussed. The result indicates that in stabilized soils, if the concentration of CH is not saturated, the added admixtures may increase the strength of the stabilized soils remarkably, so the degree of saturation of CH is lower, the amount of admixtures is more, and the increment of strength of the stabilized soils is higher; inversely, if the concentration of CH is saturated in the stabilized soils, the admixtures will be useless for the strength of the stabilized soils. In a word, admixtures can improve the strength of the stabilized soils by means of increasing the degree of saturation of CH of the stabilized soils.