Electro-optic modulator is one of the most important components for optical communication system. Its performance determines the transmission performance of an optical communication system. For the electrode, its structures, species and designs have a significant influence on the property of modulator. For designing and researching the electrode of novel electro-optic modulator based on FBG, the relationship among the overlap of mode field, structural parameters of electrode and FBG's center wavelength shift Δλ were discussed in this paper by numerical calculation methods. It has a significance of manufacture of polymer electro-optic modulators based on FBG, and promotes the development of electro-optic modulator.