The invention discloses an automatic stop device for vacuum oil filling of a transformer. The automatic stop device comprises a bracket, a first reed pipe, a first buoy, a second reed pipe, a second buoy and a flange disc, wherein the bracket is fixed at the lower part of the flange disc; the first reed pipe and the second reed pipe are respectively fixed on the bracket from top to bottom; the first buoy is positioned at the lower part of the first reed pipe and is hinged with the bracket; the second buoy is positioned at the lower part of the second reed pipe and is hinged with the bracket; and magnetic pieces are arranged on the first buoy and the second buoy. The automatic stop device is arranged at an opening of the top of the transformer, when the transformer is subjected to vacuum oil filling, an alarm is given according to the oil level so as to stop filling, the defect that the core of the transformer is affected by damp due to low oil level can be effectively prevented by using the device, and the service life of the transformer is prolonged; in addition, the phenomenon of oil leakage due to high oil level during oil filling can be avoided, the oil consumption of the transformer can be reduced, and the oil filling equipment is prevented from being damaged.