Abstract：The characteristics of the rock strength and failure under triaxial compressions are theoretically analyzed in detail with the twin shear theory and the results are compared with experimental data. The research work shows that on the aspect of rock strength，the analytical results match the experimental data very well，but on the aspect of fracture orientations，there are some differences between analytical results and experimental data. The main reason may be that the fracture orientations are more sensitive to the inner micro-structures of rock and the condition of testing surface than the strength. However，as one kind of macro-strength theories，the twin shear theory is still an effective tool in analyzing the rock failure and strength under multi-axial stress condition，and it also has many other profits such as simplicity in formulae and convenience for use in practice.
