In order to obtain the mechanical properties and energy evolution characteristics of granite under different moisture conditions, triaxial compression tests were conducted to analyze the mechanical properties and the evolution of the dissipated energy ratio of both dry and saturated specimen, and to predict its damage stress. The results show that as the confining pressure increases, the peak deviatoric stress, elastic modulus, characteristic stress, and energy density (total energy, elastic energy, and dissipated energy) of the granite gradually increase, and the failure mode converts from tensile splitting to a shear-tensile composite. Comparing the mechanical properties of dry and saturated specimen, it is shown that saturation will lead to obvious deterioration of granite. The energy density evolution curve of granite can be divided into compaction, linear elastic deformation, stable crack propagation, unstable crack propagation, and post-peak failure stages. The ratio of dissipated energy to total energy is defined as the dissipated energy ratio, and the damage stress is predicted based on the minimum of the dissipated energy ratio. The predicted values agree well with experiment data.