An exemplary air filtering system is for filtering air passing through a ventilating opening of an electronic device casing. The air filtering system includes an air filtering unit, an actuating unit, and a monitoring and controlling unit. The air filtering unit includes a flexible air filtering mesh, a driving shaft and a following shaft. The driving and following shaft are rotatably positioned at opposite sides of the ventilating opening. The air filtering mesh is wrapped around the driving and following shafts with opposite ends thereof positioned to the driving and following shaft respectively. A portion of the air filtering mesh between the driving and following shafts covers the ventilating opening. The actuating unit is connected to the driving shaft of the filtering unit. The monitoring and controlling unit is configured to monitor a temperature in the electronic device casing and control the actuating unit according to the temperature.