The invention discloses a self-expanding anchor rod and a preparation and use method thereof. The self-expanding anchor rod is composed of a rod body, a self-expanding body mounted on the rod body, areverse anti-skid device mounted at the front end of the rod body, and a locking device located at the rear end of the rod body. The self-expanding body is constituted by a grain, a grain fixing device and a grain sealing waterproof device. The self-expanding body anchor rod is formed by the well-made grain, the rod body, the reverse anti-skid device, the locking device, a self-expanding body fixing device and the grain sealing waterproof device which are assembled. During using, the elastic waterproof protection sleeve is released firstly, then the anchor rod is soaked in water, then the elastic waterproof protection sleeve is re-arranged in a sleeving mode, the anchor rod is inserted into a drill hole, an expanding agent in the grain reacts to generate the expanding pressure to squeeze the outer wall of a sleeve of the grain to be damaged, and a dense and high-strength anchorage body is formed together with the hole wall of the drill hole to provide high anchorage force for surrounding rock of a roadway.