Investigating the dilatancy of host rock during stress re-distribution is of great sig¬nificance for underground engineering, especially underground salt cavern storages. To formulate the dilatancy variation, some measurements were conducted via unloading tests with ever-reduced confining pressure and constant axial pressure. The results demonstrated that the initial confining pressure had little influence on the dilatancy of rock salt. A larger axis pressure can promote the dilatancy of rock salt. A higher temperature would accelerate the dilatancy rate and augment the total volumetric expansion. A dilatancy-damage model was established by using theoretical deduction and numerical fitting, which showed a good agreement with test data.