The tunnel excavation destroys rock stress state and when concentrated stress exceeds the strength of surrounding rock, the tunnel periphery rocks will be destroyed. And the effective bearing ring will be soon instable and it needs to be supported. Blot-grouting support is an active support method which organically combines shotcreting support and grouting consolidation and its theoretical research achievements are less. This paper, starting from catastrophe theory, established catastrophe instability model of blot-grouting support body and it also obtained the mechanic judgment criterion of blot-grouting support body damage and the regular pattern of the point (N, q)’s motion tract in the controlling space, of which the influence to the rock stability. And the paper also judged the minimum thickness of blot-grouting support body in the point of catastrophe stability model to provide the basis for theoretical calculation and engineering application.