Abstract: Monodispersed polystyrene microspheres with 8.21 μm were prepared successfully by dispersion polymerization process. The dispersion coefficient of most particle sizes (PS) could be controlled within 0.04 and crosslinked degree was about 12.6%. The major factors that affect the particle size and size distribution were investigated such as the dosage and mode of adding DVB crosslinked agent, concentrations of monomer, initiator and stabilizer, and ascorbic acid. It is concluded that, the prepared polystyrene microspheres have good mono-dispersion, low dispersion coefficient, large particle size and highly cross linked degree under the following appropriate synthesized process. The mass fraction of styrene monomer is 28.8%~33.5%. The mass ratio of initiator: azodiisobutyronitrile and St is 0.03~0.06. The mass ratio of stabilizer: polyvinyl-pyrrolidone and St is 0.5~0.8. DVB crosslinked agent is add in the solution drop by drop, the mass ratio of cross linked agent: divinylbenzene and St is 0.02~0.08. DVB should be released completely within 2 h after the reaction began to 6 h.