To improve the bulk density and fluidity of nitroguanidine (NQ), spherical NQ crystal was prepared by spray crystallization method using N-methyl pyrrolidone as the solvent of NQ, anhydrous ethanol as a nonsolvent, nickel nitrate as crystal control agent. The optimal processing conditions of preparing high bulk density spherical NQ determined by single factor method were room temperature, volume ratio of solvent and nonsolvent of 1:10; mass fraction of the crystal control agent, spray pressure, bounce frequency and stirring speed were 0.5%, 0.6 MPa, 40 Hz and 450 r·min^-1, respectively; when spray finished, ultrasonic vibration should be continued for another 20 min. The optimal spherical NQ was analyzed by standard container method, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results show that the prepared NQ is spherical and the bulk density is 1.232 g·cm^-3, which is improved by 0.943 g·cm^-3 compared with raw material NQ, decomposition temperature determined by DSC is 258.71 ℃, which is improved by 8.03 ℃ compared with that of raw material NQ.