The invention provides a closed type compressed air and low-pressure water premixing self-rotating water mist fire extinguishing device. The fire extinguishing device comprises an air and water mixing fixed pipe, a compressed air pipeline, a water supply pipeline, air and water automatic control valves, a compressed air and water premixer, an automatic rotating shell, a rotating sealing component, a plurality of L-shaped bent spray rods and a plurality of open type compressed air and water nozzles, wherein the air and water automatic control valves are arranged on the compressed air pipeline and the water supply pipeline and are connected with an air inlet pipe and a water inlet pipe of the compressed air and water premixer, and trial air release valves and closed type nozzles are arranged on the air and water automatic control valves; the outlet end of the compressed air and water premixer is connected with the automatic rotating shell through the air and water mixing fixed pipe; the plurality of L-shaped bent spray rods are arranged on the automatic rotating shell; and the compressed air and water nozzles are arranged at the bottom end of the automatic rotating shell and the L-shaped bent spray rods. The requirement on a system is lowered. Normal fire extinguishing water, namely low-pressure water, is supplied by a water supply system, but the hole diameter of the compressed air and water nozzles is increased, so that the compressed air and water nozzles cannot be easily blocked, and the requirement on water quality is lowered. Compared with the existing high-pressure water mists, water mists produced by the device have the advantages that the sizes of the water mists are smaller and more uniform, the effective acting range is larger, and the fire extinguishing effect is better.