The invention discloses an automatic starting exhaust fan, which comprises a shell, wherein a dust suction cavity is arranged in the shell. A dust suction mechanism is arranged in the dust suction cavity. The dust suction mechanism comprises dust suction fan blades fixedly arranged at the left end of a dust suction shaft. The right ends of the dust suction fan blades are in power connection with adust suction motor fixedly arranged in the right end wall of the dust suction cavity. And a transverse dust suction pipeline and a longitudinal dust suction pipeline are arranged in the left end wallof the dust suction cavity. The automatic starting exhaust fan is more reasonable and ingenious in overall structure, and is very convenient to install, maintain and overhaul. The automatic startingexhaust fan is small in volume and occupies less floor space; moreover, the automatic starting exhaust fan can automatically and continuously walk, expand the cleaning range, improve the cleaning efficiency, and filter sucked air for many times, thus greatly improving the filtering cleanliness of the sucked air; moreover, the automatic starting exhaust fan has high-efficiency automation degree inthe use process, and has higher use and popularization values.