A method for installing a utility pole and arch-type underbracing has developed by using an extendable excavating unit mounted on an auger crane. The method comprises two steps of excavation that: the primary hole is excavated about 75 cm in depth by extending an arm about 80 cm diameter of the extendable excavation unit. The secondary hole is excavated to have a standard depth for erecting the utility pole. Then, orientation of the arch-type underbracing is determined for setting on the primary hole. An underbracing hook is installed to the arch-type underbracing for lifting and attaching a U-bolt temporarily to the arch-type underbracing by surround the utility pole. A lead wire of the arch-type underbracing is connected to an earth wire of the utility pole. The arch-type underbracing is tightened with the U-bolt surrounded the utility pole. The excavated soil is filling back into the gaps around the utility pole and the holes by tempering.