The invention discloses an intermediate adapter applied to a 1000 KV grounding wire and a 500 KV grounding wire of an ultrahigh-voltage substation. The intermediate adapter is characterized in that the intermediate adapter comprises a busbar board, the busbar board is provided with a first through hole, a second through hole, a third through hole, a fourth through hole, and fasteners respectively matched with the first through hole, the second through hole, the third through hole and the fourth through hole, the first through hole, the second through hole, and the third through hole are respectively connected with each single-phase grounding wire in a three-phase phase-splitting type grounding wire through the fasteners to electrically collect the three-phase ground wire as a point, the fourth through hole is connected with a leading wire through the fastener to form a public grounding plug, and the public grounding plug is used for being connected with a special grounding electrode of the substation. According to the intermediate adapter, the intermediate adapter and the conventional phase-splitting type grounding wire of the substation are effectively connected, effective fusion with the conventional grounding wire of the substation can be realized, and the replacement of the conventional phase-splitting type grounding wire of the substation in order to promote the intermediate adapter is avoided.