An air purifier comprises an air compressing pump, a clean air outlet and a shell. The utility model is characterized in that the shell is internally provided with an inner cylinder and liquid, wherein, the inner cylinder is internally provided with a comb type tube beams. A guide backflow bowl is arranged between the internal bottom surface of the shell and the lower edge of the inner cylinder. A Backflow sprayproof shield, a flow converting baffle plate and a flow converting ring are respectively arranged between the external wall of the inner cylinder and the internal wall of the shell and above the guide backflow bowl. Even dust of nano level is reserved in the liquid layer when passing through the liquid layer due to the increased dead weight caused by absorbing the liquid molecule, thus the utility has high filtrating efficiency and causes no secondary pollution. According to needs, the liquid of filtering medium can be chemical sterilizing agent capable of reacting with the toxtic and harmful components in the air or water added with reodorant. The utility model is multifunctional for purifying and sterilizing the air or renewing the air and refreshing the mind and brain of people.