In order to protect the ‘Y’ shape composite pylon composed by fiber glass reinforced plastic (FRP) for 400 kV overhead lines, the proper grounding mode needs to be configured to conduct the lightning current. According to the structural characteristics of FRP cross-arm, the grounding cable going down through the hollow FRP tube and the pylon tower body is proposed. The distribution of electric field and the maximum electric field amplitude in and around the fully composite pylon are simulated by COMSOL multi-physics field. Light and superhydrophobic filling materials with ablative aging resistance and high mechanical strength are prepared. The fixed grounding wire connection fittings structure is designed and its mechanical strength is evaluated under lightning stroke. Finally, the anti-flashover performance of the tower with this grounding mode is evaluated by the lightning impulse discharge test of the proportional model pylon head.