The invention relates to an earth switch assembly unit and a high-speed earth switch thereof. The high-speed earth switch comprises a sulfur hexafluoride arc extinguishing device arranged in an airtight air chamber of a casing of a corresponding assembly unit in use, wherein the sulfur hexafluoride arc extinguishing device comprises a static-end assembly unit and a moving-end assembly unit. The static-end assembly unit comprises a static arc contact and a static-end conductor electrically connected to a corresponding single-phase loop in use, wherein the static arc contact is fixedly and electrically connected onto the static-end conductor, a conductive support is fixedly and electrically connected onto the static-end conductor, and a central conductor connecting structure for being fixedly and electrically connected with a central conductor is arranged at one end of the conductive support, away from the static-end conductor. The moving-end assembly unit comprises a moving-end support and a moving arc contact for being closed up with the static arc contact to enable a single phase to be earthed. The high-speed earth switch further comprises a power output end and an operating mechanism in driving connection with the moving arc contact. The high-speed earth switch is used for extinguishing secondary arc current and used for the earth switch assembly unit.