Abstract: An air-cooled refrigerator and a control method, a control system and controller for defrosting thereof are provided. The high-temperature air of the air-cooled refrigerator exchanges heat with the evaporator in the air duct and is sent into a refrigerating compartment through the operation of a fan; when the evaporator is gradually frosted, the heat-exchanged air suffers the resistance from the frosts on the evaporator during the flow and the fan slows down. Based on this principle, the fan speed can directly correspond to the frost accumulation mass of the evaporator. The actual frost accumulation mass of the evaporator can be directly determined by determining the fan speed. When the fans peed is decreased to a certain low speed, it means that there is much frost on the evaporator and the defrosting needs to be started timely.