The invention belongs to the technical field of integral joints of cooperative robots, and particularly relates to an internal wiring tensioning mechanism for an integral joint. The internal wiring tensioning mechanism comprises a housing, a first gear, a second gear, a screw, a nut and a pull rod, wherein the first gear, the second gear, the screw, the nut and the pull rod are placed in the housing; threading holes used for threading a guide line are formed in the two ends of the housing, the first gear is installed at the threading hole on one side through a first bearing, and the two ends of the screw are connected with the two ends of the housing through second bearings; the screw is sleeved with the second gear, and the second gear is engaged with the first gear; the nut is matched with the screw to form a thread pair; and one end of the pull rod is connected with the nut, and the other end of the pull rod is fixedly connected with the guide line. The internal wiring tensioning mechanism is installed at the tail end of the integral joint, has the characteristics of simple installation and guide line passive tensioning realization without active control, and can prevent the problem of snapping of the integral joint due to guide line twining in the rotating process of the integral joint.