The effects of RDX particle size on properties of CMDB propellant including mechanical property,combustion property, sensitivity property and energy property were studied. The results show that when RDX particle size changes from 92.02 μm to 17.35 μm,corresponding maximum tensile strength of CMDB propellant is enhanced by 54% at high temperature (50 ℃) and the elastic elongation is enhanced by 85% at low temperature (-40 ℃) respectively. Meanwhile,the burning rate of propellant at different pressure increases by 11.5% at its maximum. The characteristic height of impact sensitivity increases 5.1 cm,and the explosion percentage of friction sensitivity decreases by 75%.