Rock material strength will degrade with the damage in the rock failure process. This paper reports one self-designed method to test rock strength degradation and introduce the technical routine, sample preparation (including its key technique) and experiment procedure in details. Through self-designed direct shear tests by XJ-1 portable type of shear apparatus, the relationships between shear stress and compressive stress of irregular rock samples which are produced in normal uniaxial and biaxial compressive experiments were obtained. Comparing the Coulomb strength curve gained by the direct shear tests with the ultimate Mohr circle envelope obtained from previous uniaxial and triaxial compressive experiments, it can be seen that the cohesion result measured by uniaxial and triaxial experiments before failure is obviously greater than that obtained by direct shear tests of irregular rock blocks. This difference mainly results from the damage in the rock failure processes of uniaxial and triaxial compressive experiments, not the deviation by the different testing methods.
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