The invention discloses an automatic dehumidifier for a concealed-type cable channel, belonging to the technical field of electric power protection devices. The dehumidifier comprises a cover body with both ends open. The lower end of the cover body is communicated to a cable channel. The upper end of the cover body is provided with a rainhat. The sidewall of the cover body is provided with a fan. A humidity sensor, which is used to detect the humidity inside the cable channel, is installed on a sidewall of the lower end of the cover body. A motor of the fan is provided with a control module which is inductively activated with the humidity sensor. The humidity sensor transfers a detected signal of the humidity inside the cable channel to the control module. When the humidity inside the cable channel is higher than a pre-determined value, the motor of the fan is started to ventilate and dehumidify the cable channel by the control of the control module. By use of the automatic dehumidifier, the ventilation effect inside a cable channel is improved, the humidity inside the cable channel is reduced, cables inside the cable channel are protected from being damaged, and hidden safety problems of the electric power operation are reduced.