Abstract：According to the phenomena that elastic modulus is reduced and plastic strain increased while rock is compressed，the math model of rock damage is set up. The parameters of peak on curve of stress-strain are analyzed，so that invariables of rock can be calculated by test result. Comparing two different models，it is proved that the relationship between stress and strain is completely the same，while the definition of damage variable is discretional. It means that different definition of damage variable may be equivalent. The conclusion is that whatever the essential of damage is，there is a damage variable to correspond a stationary energy release rate of damage. The damage rate and energy release rate of damage are analyzed for the compressing process with stationary strain rate and the character of acoustic emission is explained as rock specimens are compressed.
