The modified two-step seeded swelling polymerization was used to prepare monodisperse, high cross-linked and porous poly(glycidyl mthacrylate-co-ethylene dimethacrylate) (PGMA-EDMA) microspheres with polystyrene beads as the seeds, which were prepared by dispersion polymerization. Several factors including various stabilizer, ratio of activator and seeds, swelling multiples and different porogens were investigated to further enhance the characteristics of microspheres. Electron microscope, scanning electron microscope (SEM), and infrared spectroscopy (IR) and high performance liquid chromatography (HPLC) were used to test the properties of the microspheres. The results indicated that the monodisperse PGMA-EDMA microspheres with 5 um and 10 um could be obtained satisfactorily when the PS seeds were 2 um and 4 um, the ratio of activator and seeds was four times, the swelling multiples was 20-40 times, the volume ratio of cyclohexanol and toluene as porogens was 6/4, 0.2% hypromellose was the stabilizer.