After the agglomerated boron particles were sieved,the loose and the tap bulk densities for different sizes of agglomerated boron particles were determined,and the microstructures of agglomerated boron particles were obtained by scanning electrical microscope. Results show that the diameter of boron particles and the loose and tap bulk density increase after agglomerated for amorphous boron powder,and both of the loose bulk density and tap bulk density decrease firstly and then increase when the diameters of agglomerated boron particles decrease. The tap bulk density is the smallest when the diameter of agglomerated boron particles is in the range of 0.25-0.30 mm,meanwhile,the tap bulk density is the biggest when the diameter of agglomerated boron particles is in the range of d≤0.104 mm,and the loose bulk density is the smallest when the diameter of agglomerated boron particles is in the range of 0.30-0.84 mm,at the same time,the tap bulk density increases faster than the loose bulk density.