Least mean standard fitting deviation is used as an evaluation index; we analyze the applicability of five conventional triaxial strength criteria to describe the nonlinear strength characteristics of rocks based on test data of ten rocks cited from public literatures. It is obvious that linear Mohr-Coulomb criterion can’t describe the nonlinear strength characteristics of rocks. Parabolic Mohr-Coulomb criterion can describe the nonlinearity feature of rock strength; but for the reason that the fitting error is very great and the parameters from calculation is not consistent with the real data; so it is not suitable to apply parabolic Mohr-Coulomb criterion in geotechnical engineering. For the nonlinear strength characteristics of rocks at low-to-moderate confining pressure level（ ）

the Bieniawski criterion with a single parameter and Hoek-Brown Criterion is better than Bieniawski Criterion with two parameters; their fitting accuracy is close to exponential strength criterion with three parameters; but they can’t be used at high confining level. When nonlinear strength characteristics are very significant under high confining pressure

the fitting deviations of Bieniawski criterion with three parameters and exponential strength criterion with three parameters are smaller; so they can be used to evaluate the strength under high geostress