Abstract: To investigate the characteristics of strength，deformation and damage properties of brittle rocks under cyclic loading and unloading conditions of different stress，rock mechanical tests with various of stress paths corresponding as the uniaxial compression test，triaxial compressive test，uniaxial and triaxial cyclic loading and unloading test are carried out on the diabase specimens from Macheng iron mine，to obtain the strength，deformation properties and the characteristics of complete stress-strain curve of brittle rock under cyclic loading and unloading conditions.A kind of relative strain damage parameter in the process of cyclic loading and unloading test，combined are presented.Combining with the existing damage mechanics theory，the damage evolution of brittle rock are researched in the process of failure.The laboratory investigation shows that:①The peak strength of cyclic loading and unloading test is 10%~20% lower than the average uniaxial compressive strength，while the peak strength appears discreteness under triaxial conditions.②The variation trend of elastic constants is closely related to the damage mechanism of microcrack closed，open and expansion of rock under cyclic loading and unloading conditions.③The extent of damage accumulation inside the rock increased with the increase of cycles and the absolute strain damage parameter are little affected by confining pressure，while radial relative strain damage parameter is influenced much by confining pressure.

Key words: Rock mechanics, Brittle rock, Uniaxial compression, Cyclic loading and unloading, Strain damage parameters