Mathematic treatment of particle size distribution in solid propellant is presented, and the particle size distribution of aluminium powder and combustion residue of Al-containing propellant are taken as examples to be analysed by means of commonly used theoretical distribution functions,including normal distribution, lognormal and K-distribution, in statistic analysis of partical size data. On the basis of Culick’s damping model the effect of particle size distribution on instable combustion in rocket motors are evaluated and discussed.