In this study, numerical and experimental study for the packing and burning of composite solid
propellant is presented. A mathematical model which describes the unsteady burning of a
heterogeneous propellant by simultaneously solving the combustion fields in the gas phase and the
thermal field in the solid phase with appropriate jump condition across the gas/solid interface is
developed. The gas-phase kinetics is represented by a two-step reaction mechanism for the
primary premixed flame and the primary diffusion flame between the decomposition products of
the HTPB and the oxidizer AP. The propagation of the unsteady non-planer regression surface is
described, using the Essentially-Non-Oscillatory (ENO) scheme with the aid of the level set
strategy. Moreover, an experimental investigation for similar sample of 200 microns AP particles
with 50 microns AP particles imbedded in a matrix of HTPB is performed. The results show that
the large AP particle diameter has a great effect on the combustion surface deformation and on the
burning rate as well. Moreover, the effect of various parameters on the surface propagation speed,
flame structure, and the burning surface geometry is obtained.