Abstract: The classification of the grade of shrink and expansion for the expansive soils was the initial and essential work for engineering construction in expansive soil area.Based on the principle of Mahalanobis distance discriminant analysis,a classification model of expansive was established in this paper,including five indexes reflecting the shrink and expansion of expansive soil: content of clay grain,content of silt grain,liquid limit,plastic limit and plasticity index,.Linear discriminant functions were obtained through training a large set of expansive samples.It was shown that the classification model of distance discriminant analysis performed excellently with high prediction accuracy and could be used in practical engineering.