In this paper,the equilibrium states of combustion products and their thermodynamic parameters of different KNO₃/S/charcoal compositions are calculated in least free-energy principle. Using reaction kinetics theory,the simulated results and the mechanism of combustion were analyzed qualitatively. Based on explosive temperature,powder force and products,low-polluted,low-eroded ingredients of black powder were designed. An optimized black powder was compared with normal black powder in combustion products and pressure histories.