The invention provides a warning device, an ultrahigh warning system of a hot-metal bottle and a prewarning method, and relates to the technical field of blast furnace hot-metal bottle operation and monitoring. The ultrahigh warning system of the hot-metal bottle comprises a warning device, a blast furnace and a conveying line, wherein the conveying line passes below the blast furnace, and a thermal baffle is installed at the bottom of the blast furnace. The warning device comprises a cross beam, two switches, an alarm, a support seat, a swing piece, an elastic mechanism and a first elastic piece, wherein the cross beam is installed on a hearth of the blast furnace; the alarm is electrically connected with the switches; the support seat is connected with the cross beam, and the two switches are respectively arranged on two opposite sides of the support seat; the top end of the swing piece is rotatably connected with the support seat; the elastic mechanism is installed on the swing piece and can be elastically abutted with the support seat; the swing piece is provided with a first position in which the elastic mechanism is abutted with the bottom surface of the support seat and a second position in which the elastic mechanism is abutted with the side surface, which faces one switch, of the support seat, and the switch is touched and started by the swing piece. An alarm can be given when a ladle nozzle of the hot-metal bottle is ultrahigh.