The uniaxial seven stress levels cyclic loading and unloading test for salt rock and marble were carried out on MTS815 Flex Test GT rock mechanics test system, and the damage unloading modulus were discussed. The loading test wave for low cyclic loading test was sine wave，and its frequency was 1.0 Hz. The maximum of cyclic stress was less than the value of the average intensity of compression, and the cyclic number of every level cyclic stress was 30 cycles. The test showed that the hysteresis loop of the curve of strain and stress was the ribbon for salt rock and tine lobation for marble stone. The salt rock had larger irreversible deformation at reloading and unloading position where corresponding elastic deformation response was slow, but the results for the marble stone were contrary. Because the unloading modulus for salt rock was influenced by test method, the changing tendency of unloading modulus for salt rock during the two test methods was reverse, while the results for marble stone were consistent during the two test methods. The effect on the increment of irreversible deformation for salt rock was more prominent for the condition of the loading stress amplitude than that of the cyclic numbers. The damage variable test results revealed that it was more authentic to describe the damage property through the damage elastic modulus which was tested by the low cyclic loading test method for rock with marked visco-plastic deformation.
