The invention discloses an air purifier for automatically collecting dust. The air purifier is characterized in that the external part of the air purifier for automatically collecting dust is a long tubular body, wherein the air purifier mainly comprises a dust filter cone, an air inlet, a single-plate valve, a flat valve, an enclosed box, a cylinder, an ash containing barrel, an air regulating switch and a plastic pipe; the dust filter cone is arranged in a cylindrical housing; the air inlet is formed in the upper side surface; the single-plate valve, the flat valve and the enclosed box are arranged at an ash outlet, which is connected with the single-plate valve, at the bottom of the cone; the ash containing barrel is arranged in the enclosed box; and the dust filter cone is driven to rotate by an electric motor.