The invention discloses an external cable follow-up device for electrical transformation equipment for tunnel excavation, and relates to the technical field of power supply of the electrical transformation equipment. The external cable follow-up device comprises a winding and unwinding device and a weight measuring device, the winding and unwinding device comprises a winding drum, a motor and a counter, the motor is used for driving the winding drum to rotate, a counting hole is formed in the winding drum, the counter is used for counting when the counting hole rotates over the position of the counter, a force measuring device comprises a weighing device and a bearing roller, the bearing roller is rotatably arranged at the top of the weighing device, a cable is arranged on the winding drum in a winding mode, a position, close to one end connected with the electrical transformation equipment, of the cable is arranged on the bearing roller, the weighing device is used for detecting downward pressure applied to the weighing device by the bearing roller and a power transmission section, the external cable follow-up device further comprises a controller, and the weighing device, the counter and the motor are all electrically connected with the controller. The external cable follow-up device is mainly used when a tunnel is excavated by a drilling and blasting method for deslagging, the external cable of the electrical transformation equipment can be automatically wind and unwind along with the reciprocating movement of the equipment, and electric shock accidents caused by the fact that the cable is dragged to be damaged or the cable is wound into a chassis are avoided.