This study was carried out to predict the burning rate of composite solid propellant through the burning mechanism. In this investigation, specific heat, thermal conductivity and viscosity of flame gas mixture were treated as dependent variables of propellant compositions and flames. The diffusion flame height was assumed to be proportional to the only distance between ammonium perchlorate（AP） particle and binder. For the aluminized propellant, aluminium(Al) was assumed to act as heat sink until the ignition of Al, thereby flame temperatures were corrected in energy balance.
The burning rates of the propellants that were prepared with carboxyl or hydroxyl terminated polybutadiene as a binder, AP as an oxidizer and Al as a metal fuel, were measured by strand burner method.
In a bimodal AP composite propellant, the decreasing gap of the burning rate became smaller as the amount of coarse AP was increased. When the amount of AP contained from 62 % to 70 % in the propellent, the pressure exponent was suddenly increased as AP content was decreased.