The present invention provides an air filter including a main body, a pressure fan, a filter mode and a fixing assembly. The main body has a containing room, an entrance hole and an exit hole. The pressure fan is disposed in the containing room. The filter mode comprises a first filter layer, a second filter layer and a frame body. The first filter layer is disposed in the entrance hole, and the second filter layer is disposed in the frame body. As such, users can select to use only the first filter layer or both filter layers at one time. Moreover, users only need to let the frame body pivot to a position away from the entrance hole so that users can change the filter layers faster and easier.