Abstract: Taking sandstone as the research object, the damage characteristics and evolution laws of brittle rocks under graded cyclic loading and unloading are studied through graded cyclic loading and unloading tests. Based on the test results, the damage values are defined and the damage constitutive models for loading and unloading stages are derived. The results show that the proposed constitutive equation of rock damage under cyclic loading and unloading has a high fitting degree with the experimental stress-strain curve, which proves its rationality and applicability. The damage constitutive model and the defined damage value can correctly reflect the damage evolution process of rock and describe each stage of rock failure. The sensitivity of parameters has different effects on the constitutive model.