In the AC system, the regulation of dielectric constant of GIL insulator is by a great number of studies. Recently, a large number of researches has emphasized the functionally graded material (FGM) (Kato, 2006; Hayakawa, 2016). The FGM insulators that have the characteristic of spatial permittivity (ɛ-distribution) can be processed through 3D printing technique, the lamination and the centrifugation method. Through flashover test under lighting impulse voltage, it can be found that the breakdown voltage (BDV) of FGM insulator is significantly higher than conventional insulator.