The circular chamber rockburst under uniform confined pressure occurs and ends by the phase of the plastically deforming localization of rock ring in softening zone on the traditional meaning. The carrying force in the concentration zone of plastic deformation reduces under limiting state

but comparatively intact part in rock ring unloads by way of elasticity. The rockburst occurs when the elastic energy released by latter is more than the dissipated energy by former in plastically deforming form. The catastrophe model of tunnel rockburst is established forthright by the relationship between equivalent stress and equivalent strain

and state variable is expressed by softening zone radius R. Analysis shows: The occurrence condition of rockburst has relations with the product of the rock’s ratio of elastic modulus to descending modulus and crack growth degree of rocks. To rock with specific rockburst tendency

there is corresponding critical depth of softening zone

i.e. rockburst occurs when softening zone depth reaches . The amount of earthquake energy that released by rockburst has also relations with the deepening degree of softening zone.