Abstract: Rock brittleness is an important parameter to characterize failure characteristics of rocks. An accurate brittleness evaluation method is of great significance to geotechnical engineering. In the present study, we primarily summarized a considerable number of methods that were widely used to characterize rock brittleness based on the stress-strain curve. Then, three types of rocks were used to analyze the energy evolution law and brittleness index of the pre-peak and post-peak during rock failure. The results indicate that the dissipative energy evolution law of sandstone, marble, and granite specimens under uniaxial compression presents "Ɔ" type, "S" type, and "L" type respectively; At the pre-peak stage, the brittleness index of marble is the smallest and that of the granite is the largest; At the post-peak stage, the brittleness index of sandstone is the same as that of granite, and that of marble is the smallest; The full stress-strain curve can better characterize the brittleness pre-peak and post-peak in the process of rock failure based on the energy evolution. While the pre-peak and post-peak indexes cannot be simply mathematically characterized into one index. The correlation between the pre-peak and post-peak rock brittleness indexes is not clear. The combined brittleness index cannot effectively characterize the change of the pre-peak and post-peak brittleness at the same time. Pre-peak and post-peak brittleness indexes should be separately considered. The brittleness characteristics and laws of the pre-peak and post-peak should be separately characterized and analyzed.