Abstract: Influence of five kinds of coupling agents on the wetting property of glass fiber and on the dielectrical property of glass fiber/epoxy composite interface was studied. The results show that after glass fiber being treated with coupling agents and activation energy of glass fiber for wetting being decreased, the reaction activity and wettability between glass fiber and epoxy resin matrix can be improved. A good interface adhesion of glass fiber/epoxy results in an improvement of dielectrical propertys of glass fiber/epoxy composite interface. Its improvement range depends on the polarity and chemical structure of the coupling agents.