The invention provides a falling prevention quick-opening and slow-descending device and a falling prevention quick-opening and slow-descending method for climbing a pole tower in a power system, and belongs to the field of safe devices for climbing poles. The falling prevention quick-opening and slow-descending device comprises an accommodation bag, wherein a trigger device is arranged on the accommodation bag; a high-pressure gas cylinder or a steel cylinder filled with chemical substances for quickly generating light gases is arranged on the trigger device; an air outlet hole of the trigger device is connected to an air inlet hole of an air bag arranged on a parachute; the parachute is accommodated in the accommodation bag, and four corners of the rectangular parachute are connected to the bottom of the accommodation bag through connecting ropes; and a rope is connected onto the operating end of the trigger device and can be used for emergency rescue when a worker is dangerous in the process of climbing the pole.