Abstract Ammonium Perchlorate (AP) is frequently employed in the form of bimodal mixtures as an oxidizer in composite propellant formulations. Hydroxyl Terminated Polybutadience (HTPB) is also frequently used as a prepolymeric fuel binder in these propellants. The combustion behavior of this heterogenous mixture depends on both packing density and specific surface area of the oxidizing particles. One of the reliable packing models has been selected and employed for calculating the packing parameters of many of monomodal and bimodal mixtures. A one dimentional lab scale vibrator has been employed for measuring the packing density. A remarkable agreement has been detected between the calculated and the experimentally obtained values. Packing factor of about 0.64 and 0.82 has been recorded for the monomodal and the bimodal mixtures respectively. One of the efficient two dimentional combustion models has been selected and employed for predicting the flame structure and the regression surface for some selected propellant formulations. The results prevailed the important role of the packing parameters regarding both the flame structure and the regression surface