The invention discloses a gun piece used for launching a fire extinguishing bullet. The gun piece comprises a muzzle brake, a barrel and a gun breech which are connected in sequence, an inner chamberof the barrel is divided into an explosive room part, a chamber throat part and a rifling part from back to front, the outer surface size of the barrel is gradually reduced from back to front, a latchroom vertically opened is arranged in the middle of the gun breech and used for containing a breech block and providing a guide rail for vertical moving of the breech block, and the muzzle brake is aporous single-air-room structure. The indirect aiming function is used for remotely emitting a fire extinguishing agent, the structure is reliable, projectile filling and launching can be ensured, during launching, the bullet is matched with high temperature, high pressure, and high-speed explosive gas, the gun piece is used for launching the fire extinguishing bullet, the initial velocity and the flying direction are given to the projectile, remote-distance precise pressing is carried out on the fire of a fire scene, time from fire to the fire extinguishing taking measures can be shortened,and spreading of the fire can be reduced; and under the condition that the fire scene is free of intervisibility, remote forest fire extinguishing function is achieved, and the gun piece is suitablefor fire extinguishing guns of various medium calibers.