Self-cleaning exhaust fan

The invention discloses a self-cleaning exhaust fan which comprises a shell, an air duct, an air inlet mesh enclosure, an air outlet mesh enclosure, a motor cylinder, a motor, a transmission shaft and an impeller, wherein a rainwater flow channel is arranged in the shell; a rainwater outlet and a rainwater collecting port communicate with the the rainwater flow channel; a water drainage flow channel is arranged in the shell; a water drainage port combination and a water outlet communicate with the water drainage flow channel; rainwater can be drained to the air inlet mesh enclosure through the rainwater collecting port, the rainwater flow channel and the rainwater outlet, the air inlet mesh enclosure can be washed and cleaned through the rainwater, and then dust on the air inlet mesh enclosure can be reduced; wastewater can be drained to the outside world through the water drainage port combination, the water drainage flow channel and the water outlet; compared with the prior art, the self-cleaning exhaust fa