In the aim of exploring the damage evolution of rock under load in the process of failure, the deformation and failure process of half-homogeneous sandstone are studied through triaxial compression test with acoustic emission monitor. The acoustic emission characters of sandstone in different stages of triaxial compaction under different confining pressures are analyzed. As confining pressure increases, acoustic emission activity weakens, which indicates that confining pressure could inhibit the emergence and development of internal crack and improve the strength of sample, and consequently delay the time of macroscopic damage. Furthermore, a new damage variable and damage evolution model is proposed based on AE events by assuming that the damage evolution equation obeys Weibull distribution and lognormal distribution, and a correction coefficient is introduced to modify the damage variable. The damage development of sandstone is mainly divided into four stages the stage of initial damage, the stage of steady development, the stage of accelerative development and the stage of damage after failure. By comparing the two acoustic emission damage models, we found that logarithmic normal distribution is more suitable for describing acoustic emission phenomenon of half-homogeneous sandstone.