The paper discussed the principles of PRK(Photorefractive Keratectomy) and LASIK( Laser in - situ keratomile-usis), mechanism of action of excimer laser on cornea ,mode of laser delivery to the cornea , relationship between the ablation rate and the energy of the excimer laser and the " flying - spot" scanning technology. The results of this paper have been applied to ophthalmic excimer laser system . During clinic practice , it has achieved satisfied outcomes.