Abstract: The mechanism of strength for anisotropic internal friction materials is studied here by means of the standard space theory of solid mechanics. A generalized strength criterion is given, in which the number of strength coefficients is equal to that of anisotropic subspaces of material. In isotropic case, it degenerates into the generalized Mohr-Coulomb’s Model. The formulae of strength criterion for common anisotropic materials are deduced and the method to determine the strength coefficients is presented. Finally,a calculating example is given and compared with the results of the existing strength model.