Respirator capable of preventing back flow

The invention discloses a respirator capable of preventing back flow. The respirator comprises a casing, an air inlet pipe, an air outlet pipe and a sealing ball, wherein an inner chamber of the casing is divided into an upper chamber and a lower chamber, and the bottom wall of the upper chamber is in a taper shape narrowing from top to bottom; a channel extending to the bottom of the lower chamber is arranged at the lower end of the bottom wall of the upper chamber, and a gap is reserved between the lower end of the channel and the bottom wall of the lower chamber; the air inlet pipe is arranged on the casing and communicated with the upper end of the lower chamber; the air outlet pipe is arranged on the casing and communicated with the upper chamber; the sealing ball is movably placed at the upper end of the channel. When the pressure of the inner chamber of an engine is smaller than the barometric pressure, the sealing ball can be pressed at the upper end of the channel by the barometric pressure, so that outside air can be prevented from entering the inside of the engine, the fault of the engine is reduced, and the service life of the engine is prolonged.