The invention discloses an anti-collision automatic braking protection device of a motor vehicle. The protection device can enable a back magnet on a back anti-collision beam of a front vehicle to apply magnetic repulsive force homopolar with the magnet to a front magnet on a front anti-collision beam of a back vehicle so as to perform the non-contact two-stage passive deceleration or brake for the back vehicle in a certain dangerous spacing distance of the front vehicle and the back vehicle running on one track so as to realize no generation of direct head-to-head rear-end collision between the back vehicle and the front vehicle. The device comprises a front magnet, a back magnet and a box, wherein a first-stage sliding block and a second-stage sliding block are arranged in cover plate holes in a sliding manner; a button switch 1 is arranged on the first-stage sliding block; a button switch 2 is arranged on the inner wall of the box in front of a second-stage stopper; a guide column is arranged on a front anti-collision beam of a vehicle in a sliding manner; a cover plate is fixed at the front end of the guide column; the front magnet is arranged on the first-stage sliding block; and the back magnet is fixed on a back anti-collision beam. The device is mainly applied to a vehicle anti-collision protection technology.