An evaluation of fractal dimensions of both physical particle roughness and grain size distribution of agglomerated boron was determined. The relationship between the roughness and size distribution of boron agglomerate particles and the fractal dimension as well as rheological property of fuel-rich propellant were analyzed. The results show that the rougher the boron particles,the higher the corresponding fractal dimensions,and the higher the fragmentation fractal dimensions,the higher the relative percentage of fine boron particles in the size distribution. The fractal theory is applicable to quantify the irregularity of agglomerated boron particles surface and grain size distribution.