Abstract: A Series of researches on degree of aluminum agglomeration and combustion in propel-lants have been completed experimentally. The results show that AP particle size distribution is an important factor effective on aluminum combustion in propellants. It is found that the smaller AP particles are, the less the possibility of aluminum agglomeration is. This conclusionsupports the "Pocket Model", submitted by N. S. Cohen and is consistent with the results calculated with empirical formulas. The effect of bimodal AP particle size distributionis elaborated in this paper. It is suggested that the most suitable content of fine AP particle in the composition of propellants be about 40%. The result is helpful to the compositiondesign of new propellants.