The invention provides a periodic cleaning device for long-distance transmission lines, and relates to the technical field of transmission line cleaning equipment. The periodic cleaning device comprises a movable carrier, a storage bin arranged on the movable carrier, a suspension mechanism arranged on the storage bin, a spraying mechanism arranged on the movable carrier and a control mechanism which is arranged on the movable carrier and used for controlling the movable carrier, the suspension mechanism and the spraying mechanism. The periodic cleaning device can periodically clean the transmission lines in winter by adopting a special ice melting agent, and can realize the functions of patrol inspection and ice cleaning. In addition, the ice melting agent applicable to the ice melting device is provided, which is low in freezing point, high in ice melting speed in a short time, significant in ice melting effect and small in damage to carbon steel and plants.