The embodiment of the invention provides a method and device for controlling a refrigerant of an air conditioner and the air conditioner, and belongs to the field of domestic appliances. The method comprises the steps that the number of inner units which are operated in the air conditioner operation process is determined; whether the number is changed or not when the air conditioner is continuously operated for a preset period of time; on the condition that the number is not changed, the refrigerant of the air conditioner is controlled according to a superheat degree control method; and on the condition that the number is not changed, the refrigerant of the air conditioner is controlled according to an average temperature control method. The device comprises a controller. The air conditioner comprises the device. Accordingly, whether the refrigerant of the air conditioner is controlled by the average temperature control method or the superheat degree control method is determined according to the number of the operated inner units, the efficiency of heat exchangers of the inner units can be sufficiently utilized, and refrigerant distribution of the inner units is achieved.