ABSTRACT The determinations of the peak strength of rocks have been comprehensively investigated and applied to the simulation of tunneling. However, only few achievements have been made to estimate the post-peak strength of rocks, which is becoming more and more important due to the rapidly increase of tunneling depth. Understanding both the peak and the post-peak strengths of brittle rock are necessary for the design of deep tunneling. After reviews of various estimation methods, the post-peak form of the Hoek-Brown failure criterion by introducing a strength loss parameter (ß) was adopted in the paper. The relationship between the strength loss parameter (ß), the post-peak strength and the confining stress were established on the basis of the triaxial compressive tests of marble. A numerical simulation of the tri-axial compressive test was conducted by the axisymmetric modeling in FLAC to verify the accuracy of the method suggested. The post-peak strength estimation method, so-called strength loss experiment method, may estimate the post-peak strength reasonably well.