Abstract: The present invention provides a protection device for air filter, which includes a dust sensor and an air filter protector, wherein, the air filter protector includes: a dust concentration comparator adapted for comparing a level signal transmitted by the dust sensor to represent a particle concentration of dust or smoke with a reference level, so as to output a positive or negative pulse signal according to a result of the comparison; a first inverter; a pulse generator and adapted for inverting a pulse signal outputted by the first inverter; a filtering comparator adapted for converting an output of the pulse generator into a high or low level signal; a relay switch adapted for performing on or off action according to the output of the filtering comparator, so as to control opening and closing of an air valve of the air filter.