The recrystallization of AP was carried out using supercritical CO₂ as the anti-solvent and acetone as the organic solvent for AP． The effects of the main parameters including temaperature,initial concentration of the solution, the final pressure and hold time after the pressurization on the gas anti-solvent(GAS) recrystallization process were studied． AP particles (30-40 nm) with narrow size distribution are obtained at 10 MPa,40 ℃and 35 kg·h^-1． The results show that the intensity of liquid onflow have a great influence on AP average size and morphological characters in GAS，and AP crystals develope from the nuclei to sphericity,polyhedron,needles,and whiskers in GAS．