Composite solid propellant is a kind of composite material with high packing fraction. It has the characteristic of heterogeneity in meso-scale because of the random distribution of oxidizer and metal particles in the matrix. Effects of particle gradation, spatial distribution and content must be taken into consideration while studying the combustion characteristics and mechanical property of the solid propellant in meso-scale. A random sphere packing model of nitrate ester plasticized polyether propellant based on molecular dynamics method was built. Monte-Carlo simulation was used to calculate the two-point correlation function of the random sphere pack. The effects of packing fraction, particle gradation and particle size on the two-point correlation function were studied. From the statistical significance, to obtain the minimum size of representative volume element with the characteristics of ergodicity, statistical homogeneity and isotropy can effectively reduce the calculation cost of subsequent research. The meso-scale propellant model established in this research is important and basic for the study on the complex nonlinear processes of the composite solid propellant such as combustion, decomposition, agglomeration.