Rock burst is a complex dynamic impact phenomenon due to unloading.Study on the mechanism of rock burst based on unloading stress laboratory tests and damage mechanics is very important for its prediction.The triaxial unloading tests of rock samples with different pore and under different unloading velocity were done.Acoustic emission technique was adopted to monitor the stress distribution when the rock burst happened under complex stress path.And the Acoustic emission feature during the failure process was studied.The relationship between acoustic emission and damage variables were established based on statistic rules and damage mechanic theory.The mechanism of rock burst was analyzed from rock damage.It was concluded that rock breaking strength increased and rupture aggravated with the reduction of pore rates.Circumferential deformation was elastic at the beginning of unloading.Then it turned to be plastic along with the decreasing of confined pressure.The small fracture inside the rock sample extended and connected.Finally, the persistent cracks formed and leaded to failure.At the same time, the stress decreased remarkably.The magnitude of unloading velocity had an effect on the mode of crack growth and stress transfer The smaller the magnitude of unloading velocity is, the greater the expanding deformation is.At the beginning of unloading acoustic emission increased dramatically and the stress redistributed.Rock burst can be forecasted by a dramatic increase of acoustic emission parameters, which is the sign of rock rupture.