The invention discloses a quick power-off device for a high-voltage distribution network line, and the device comprises a grabbing part, an extension part, and an anchoring part; the grabbing part ismade of a conductor material, and the tail end of the grabbing part is connected with one end of the extension part; the extension part is made of a conductor material, and the other end of the extension part is connected with the anchoring part; the grabbing part is clamped on any wire on the two sides of the distribution network line, the extension part is in contact with a multi-phase wire of the distribution network line, and the grabbing part is matched with the extension part to enable the distribution network line to be short-circuited; the anchoring part is used for providing gravity and fixing the positions of the grabbing part and the extension part. The invention further discloses a quick power-off method based on the power-off device. The power off device is simple in structureand convenient to use, can instantaneously enable a high-voltage power transmission line to generate permanent interphase short circuit to cause tripping and power failure of switch protection action, effectively reduces the electric shock time of an electric shock person, and can greatly increase the survival probability of an electric shock person.