The invention discloses an entire-underground cable tunnel safety manhole being used also as a ventilation shaft, which pertains to the technical field of power supply and distribution circuits and comprises an underground firewall with a door, an aboveground firewall, a fire door, a propeller fan, a fire damper, a safety manhole, a vertical ladder, a stair hall, a sump pit and a dredge pump; wherein the safety manhole is also used as a ventilation shaft and adopts an entire-underground type. The entire-underground cable tunnel safety manhole has the advantages that: as the internal structure of the ventilation shaft is optimized, the requirements of ventilation, drainage, fire prevention and routing inspection of the cable tunnel are satisfied, and the entire structure of the ventilation shaft is arranged underground, thus solving the problem of the overall beautiful appearance of a factory and effectively reducing the construction cost. The channel and the ventilation opening of the ventilation shaft are integrated into one, thus being capable of being flexibly arranged without affecting the arrangement of other facilities on the ground in the factory district.