An air cleaner includes a housing, a fan, one or more filtering elements, and a washing system. The housing is provided with an air inlet and an air outlet. The fan is mounted in the housing at a location corresponding to the air outlet and rotated by a motor. The filtering elements are arranged in the housing below the air outlet while above the air inlet. The washing system includes a drain pan, at least one sprinkler, a water tank and a pump, is located in the housing. The drain pan is provided with a drainage port and obliquely arranged below the filtering elements. The sprinkler is arranged above the filtering elements. The water tank and the pump are mounted at a bottom of the housing. An injection pipe is connected to the water tank and extends out of the housing for filling the water tank with water and/or detergent.