This paper presents a constitutive model for simulating the swelling–shrinkage volume change of expansive soils during wetting–drying cycles. Based on the concept of the critical swelling–shrinkage state proposed by Zhao et al. [21], the elastic swelling–shrinkage deformation, plastic swelling/shrinkage deformation, and accumulative deformation during wetting–drying cycles were analyzed. Influences of the initial dry density and stress applied on the yield suction were discussed. The suction decreasing yield surface (SD) and suction increasing yield surface (SI) were defined. The variations of SD and SI yield surfaces were proposed. Calibration was performed with results of the cyclic wetting–drying tests conducted. The proposed model was validated by simulating cyclic wetting–drying tests conducted on compacted GaoMiaoZi (GMZ) bentonite. Good agreements were obtained between the simulation results and the experimental ones. Using the proposed model, influences of dry density and stress applied on the swelling–shrinkage deformation and accumulative deformation of expansive soil were well described.