In order to avoid deflagration to detonation transition during the ammunition destruction by high-energy combustion method, the internal pressure of the shell can be controlled by the fused exhaust hole on the mine shell. In this paper, the equilibrium pressure equation for the steady state combustion of the internal explosive in the open-hole shell is derived by the model referring to the zero-dimensional interior ballistic calculation method under the combustion chamber model of the solid rocket engine. According to the size of fused exhaust hole measured by mine destruction experiment, the internal steady combustion equilibrium pressure for TNT charged mine is 0.69 MPa, which is far below the literatures reported deflagration to detonation transition pressure upper limit, the calculated results are in accordance with the experiment data.