Abstract: By employing the failure curve of Hoek-Brown criterion as a failure curve in the meridian plane, as well as the triangle failure curve of a unified strength criterion as a failure pattern in the deviatoric plane of a rock, a new three-dimensional strength criterion is proposed for an intact rock. In the meridian plane, the proposed criterion is nonlinear and can simulate the effect of hydrostatic pressure well; In the deviatoric plane, the failure curves change from the MN curved triangle to the DP circle and can take account of the influence of intermediate principal stress properly. The failure surface of the new strength criterion is continuous, smooth and convex. It can be thusly employed to develop a yield function for the constitutive model of rocks. The proposed criterion has clear physical meanings and only three parameters need to be determined by experimental results, namely σ_c, m_i and m_t. By the simple determined method for parameter m_t, the parameters for the proposed criterion are reduced to σ_c and m_i, which are same as that of original Hoek-Brown criterion. The proposed strength criterion has a good agreement with the experimental data. Moreover, by introducing the the Geological Strength Index (GSI), the proposed strength criterion also can be employed to simulate the strength of rock masses.