The invention discloses a pressure relief pneumatic fire extinguishing bomb. The fire extinguishing bomb comprises a fire extinguishing bomb body filled with a fire extinguishing agent, wherein a pressure relief cabin section is fixedly connected to the tail portion of the fire extinguishing bomb body, an inflatable pressure relief opening is formed in the outer wall of the pressure relief cabin section, a high-pressure cabin section is arranged on the tail portion of the pressure relief cabin section, the high-pressure cabin section comprises a high-pressure cabin shell with a top opening, apressure control membrane is arranged at the top of the high-pressure cabin shell, a high-pressure cabin inflation port is formed in the bottom of the high-pressure cabin shell, the front portion of the high-pressure cabin shell is embedded into an inner cavity of the pressure relief cabin section in a sealed mode, and the outer wall of the high-pressure cabin shell is connected with the outer wall of the pressure relief cabin section through a breakable connecting frame. According to the fire extinguishing bomb, no initiating explosive device is used, high-pressure gas is adopted for firing of the fire extinguishing bomb and spraying of the fire extinguishing agent, the firing process is safer, potential safety hazards existing in the production, storage, transportation and use processesof the fire extinguishing bomb are avoided, a secondary fire is eradicated, and the fire extinguishing bomb is lighter than a traditional fire extinguishing bomb by adopting compressed gas driving.