Abstract: The mechanism of nano graphite powder (NGP) on improving the mechanical properties of the Guilin red clay is investigated in the laboratory with CU triaxial experiments. A series of orthogonal shear tests are conducted with the TSZ-1 triaxial apparatus. SEM is used to test the microstructure of the samples. Variance and range methods are applied to analyze the sensitivity of each factor that affects the influences on the mechanical characteristics of the modified red clay. The test results show that the NGP content is the main factor affecting the mechanical characteristics of the modified red clay, while the normal stress and the dry density are the minor factors. The normal stress difference against the axial strain curve for the modified red clay shows an overall hyperbola relationship, with the obvious peak stress, but shows the strain hardening behaviors. The shear strength of the modified red clay has a good linear relation with the normal stress, which can be described with the linear Mohr-Coulomb Criterion. With the increasing NGP content, the internal friction angle φ remains basically unchanged, while the cohesion increases firstly and then decreases. The presenting mechanical properties of the NGP-red clay is closely related to the effect of the NGP on the pore structure of red clay and the particle adhesion and cementation.