The recrystallization of ammonium perchlorate (AP) was carried out using supercritical CO₂ as the anti-solvent and ethanol as solvent. The volumetric expansion curves of CO₂-ethanol were measured and the vapor-liquid equilibrium of CO₂-ethanol system was calculated with Peng-Robinson equation. The effects of the main operation parameters on the result of the gas anti-solvent(GAS) recrystallization process were studied experimentally, such as the initial concentration of the solution,the final pressure and hold time after the pressurization. It is shown that the average grain size increases when the temperature rises. And the average grain size decreases when the initial concentration increases at 25 ℃ and by contraries at 31 ℃ and 40 ℃. Meanwhile the faster the pressure raising,the more uniform little AP grain could be produced. If the final pressure is more than 9 MPa, the increase of pressure has little effect on average size of AP particle. When the pressure is 6 MPa, the increase of hold time leads to a significant increase of the average grain size with a wide distribution. But when the final pressure is 9 MPa, there is a little change in size, only a slight change in its morphology. The effect of the intensity of liquid flow and the physical and chemical properties of the solvent itself were prevailing when compared to the effects of the other operation parameters. Finally, AP particles (60 nm, polyhedron) with narrow size distribution were obtained at 9 MPa, 25 ℃ and 35 kg·h^-1, and the phenomenon of intercrystalline fracture was found in AP particle.