The invention relates to an attachment of a centralized central air conditioner, in particular to a chlorine dioxide gasification device used for sterilizing the centralized central air conditioner. The invention solves the problems that the current chlorine dioxide gasification device used for air sterilization of the central air conditioner is low in gasification rate of chlorine dioxide aqueous solution, is inconvenient to mount and dismount and increases the blowing-in air humidity of the central air conditioner. The chlorine dioxide gasification device comprises a box body and an aeration tank positioned in the box body, wherein upper ends on two sides of the box body are provided with an air inlet and an air outlet, and lower ends on two sides of the box body are provided with a liquid inlet and a liquid outlet; the aeration tank consists of an aeration tank outer shell of which two sides are provided with a liquid inlet and a liquid outlet, and a pore plate which is provided with an air inlet and a plurality of aeration holes; and a plurality of aeration tanks can be connected in series to realize multi-stage gasification so that the gasification rate is greatly improved. The chlorine dioxide gasification device is reasonable in design and skillful in structure, is arranged outside a main air supply channel of the centralized central air conditioner, effectively solves the problem of high air-out air humidity caused by water carried by gasified chlorine dioxide, is convenient to dismount and mount, and is suitable for popularization and application.