<p>The unloading damage and the loading damage of rock were essentially different. In order to better understand the mechanical and deformation characteristics of rock under different unloading stress paths, the loading and unloading tests of three stress paths were carried out on sandstone. The relationship between the feature quantity and the deformation parameter was constructed by introducing feature quantities that could describe the deformation law of deformation parameters in different deformation stages. Then, a new unloading damage constitutive model was established to describe the stress–strain relationship of unloading rock. The results show that the main reason for the deformation and failure of the rock under the unloading path was the rapid increase of radial deformation of the rock, which led to its rapid expansion and failure. Compared with conventional triaxial specimens, the ultimate failure of the unloading test was more severe, and the radial strain generated was much larger than the axial strain. The axial strain of the unloading test was much smaller than the axial strain of the loading path. By combining Lemairte’s strain equivalence principle and the evolution Eq. of deformation modulus at different deformation stages, the established damage evolution model could better describe the damage evolution law of rock and had a good correspondence with the rock deformation stage. The model curve could better describe the stress–strain variation law of the unloading test, and also highlighted the deformation characteristics of the rock compaction stage. In the elastic front stage of the peak front, the model curve and the test curve almost coincided, and the nonlinear deformation characteristics and post-peak deformation characteristics of the late unloading yield stage were also well described.</p>