The utility model proposes a device for the on-line elimination of a fault of a high-capacity transformer core, and the device comprises a supporting insulator, a first current transformer, a second current transformer, a fault elimination circuit, a short-circuit switch group, and an AD conversion interface circuit. The exterior of the body of a transformer oil tank is provided with the supporting insulator, and the supporting insulator is provided with the first and second current transformer. An iron core grounding leading-out wire passes through a primary coil of the first current transformer, then passes through the fault elimination circuit and the short-circuit switch group which are in parallel connection, and finally reaches a grounding end. Two ends of a secondary coil of the first current transformer are connected with two input ends of the AD conversion interface circuit, and two ends of a secondary coil of the second current transformer are connected with the other two input ends. According to the utility model, the fault elimination circuit is enabled to be in a short-circuit state when a transformer is in normal operation. When a plurality of points of an iron core are grounded, the fault elimination circuit is connected. After charging, the fault elimination circuit carries out the discharging of the iron core, thereby achieving the purpose of eliminating a multi-point grounding fault of the iron core.