Aiming at the problem that the unexploded ordnance irradiated by high energy laser is easy to explode, which will cause great harm to the surrounding environment, the theory of stable combustion of shell charge under the condition of pre-opening hole iwas systematically sorted out. Based on the explosive exponential combustion law and the choking flow theory model of gas products, the pressure development model of shell charge during combustion, under the condition of limited pressure relief was established. A simplified calculation method for the combustion area of cylindrical charge was proposed. A calculation program was written based on Computational software to study the development law of the combustion pressure of unexploded ordnance charge under different pressure relief hole diameter. The variation law of the diameter of the safety relief hole and the diameter of the projectile body had been obtained. The consistency between the relevant results and the experimental results proves the correctness and applicability of the theory, which can provide theoretical support for laser combustion destruction of unexploded ordnance