The invention relates to an external auxiliary gear-shifting device for a main transformer on-load voltage regulation switch. The device comprises a portable power generation box, a fixed frame, and a control box. The fixed frame comprises two connecting plates, two clamping boards, and a motor. A motor chassis is fixed on the two connecting plates, and the connecting plates are movably connected with the clamping boards through first adjusting bolts. Two sides of the clamping boards are provided with second adjusting bolts. The tail end of an output shaft of the motor is provided with a crank port mechanism. The control box comprises an adjusting button, an AC-DC power supply, a controller, and a driver. The adjusting button is connected with the controller, and the AC-DC power supply and the controller are respectively connected with the controller. The device is reasonable in structural design, is convenient to operate, and employs a portable power generation box, which is usually carried by a power worker, to cooperate with the motor with the output shaft structure being the crank port structure. The motor is disposed on the fixed frame, and is connected with the driver. An instruction is transmitted through a button to directly drive the motor to operate. The device replaces the slow manual operation, saves time and labor, and is higher in actual operation efficiency.