Abstract: The volumetric strain of compacted expansive clays induced by cyclic wetting and drying can be decomposed into a reversible component, which changes synchronously with the suction or water content, and an irreversible component with mainly generated at the early stage of wetting-drying process. The reversible component is derived from the reversible deformation behavior of the microstructure of clay aggregates that form the soil skeleton, and depends mainly on the current suction. The irreversible component is derived from the irreversible change of the macrostructure of the soil skeleton, and is associated with the difference of macrostructure between the current and equilibrium states. The mathematical descriptions of the two components are given according to the analysis of the physical mechanism and by fitting the experimental results. A practical constitutive model is proposed for compacted expansive clays by combining the mathematical description with the BBM model proposed by Alonso et al. The proposed model has a small number of material parameters that can be easily determined. Its predictive capabilities are better than that of the BExM model through comparative simulation of comprehensive experimental data set.