Polymerization process for preparing mono-disperse organic/inorganic nanocomposite microspheres in the field of nano technology is disclosed. The process comprises preparing of two different miniemulsion systems of A with inorganic nanoparticles and B with polymeric monomers in advance; adding water-soluble initiator into miniemulsion A, stirring till complete dissolution finally, heating the mixed system to a given temperature for isothermal reaction. The grain size of the as-prepared superparamagnetic Fe3O4/polystyrene using to present invention is homogeneous and controllable, and the magnetic particles content is controllable.