Supercritical antisolvent (SAS) process is a recently developed technology to produce micro- and nanoparticles. This paper presents a continuous apparatus to conduct experiment of SAS process. With the apparatus, the effects of pressure, temperature and flow ratio Of CO2 to the solution on the shape and size of particles are studied for the quercetin-ethanol-CO2 system. Spherical quercetin microparticles with diameters ranging form 1 mu m to 6 mu m can be obtained while ethanol is used as organic solvent. The most effective fact on the shape and size of particles is pressure, the next is temperature and the last is the flow ratio of CO2 to solution.