The invention discloses a blast hole plugging device and method. The blast hole plugging device comprises a first plugging part and a second plugging part, wherein the second plugging part is near a blast hole opening and is fixed with the inner wall of a blast hole, the circumferential profile of the first plugging part and the circumferential profile of the second plugging part are matched with the hole diameter of the blast hole, the first plugging part is provided with a first surface forming an angle with the axial line of the blast hole, the second plugging part is provided with a second surface forming an angle with the axial line of the blast hole, and the first plugging part and the second plugging part mutually form surface contact through the first surface and the second surface. In the blasting process, the first plugging part moves along the second surface due to the pressure of detonation gas in the blast hole, i.e., the first plugging part and the second plugging part generate relative malposition, the first plugging part exerts the positive pressure on the inner wall of the blast hole, and the pressure of the detonation gas is greater, so the generated friction is also greater, and the moving of the first plugging part and the second plugging part towards the outer part of the blast hole is retarded through the friction force, so that the acting time of the detonation gas is increased, and a good blasting effect is achieved.