The utility model belongs to the technical field of the monitoring of transformer core ground connection, concretely relates to novel transformer core earth current monitoring device, it mainly includes power switching circuit, mutual -inductor, signal acquisition and processing unit, monitors demonstration backstage and acousto -optic warning circuit, the mutual -inductor suit is on iron core ground lead, power switching circuit's output with the input of mutual -inductor is connected, the mutual -inductor draw forth the end with signal acquisition is connected with processing unit's input, signal acquisition is connected the monitoring with processing unit's output and shows the backstage, the monitoring shows the output and the acousto -optic warning circuit connection on backstage, theutility model has the advantages of the interference killing feature is strong, and measurement accuracy is high, can monitor often and can inquire historical data and warning.