Abstract: An automatic fire-extinguishing system and method for a cable tunnel. The system includes an inspection robot, a positioning robot, and guide rails fixed on an inner top of the tunnel, where the inspection robot and the positioning robot are connected to the guide rails respectively, and the positioning robot is arranged in a groove of the inspection robot and able to be moved by the inspection robot along the guide rails; and the positioning robot is able to independently enter and exit an inner space of the inspection robot along the guide rails, and the positioning robot is configured to control a built-in fire-extinguishing mechanism to extinguish fire at a position with a preset distance from a fire source. Both fire-fighting medium docking and fire extinguishing are realized; a quick access to a battery is realized and fire-extinguishing inspection efficiency of a cable tunnel is improved.