An underwater neutral cable arranging mechanism with a movable winding drum comprises two opposite horizontally moving carriages and the winding drum installed between the two horizontally moving carriages. A guide rail is arranged on the upper portions of the horizontally moving carriages. A cable arranging mechanism body is installed between the two horizontally moving carriages and located below the winding drum. The horizontally moving carriages on the two sides are respectively provided with a set of chain wheel transmission mechanism. One set of chain wheel transmission mechanism drives the winding drum to rotate, and the other set of chain wheel transmission mechanism drives the cable arranging mechanism body to rotate. A tail mandrel on a nut swing link in the cable arranging mechanism body is embedded in a radial cylindrical hole of a fixed sliding block. The fixed sliding block is fixedly connected with a repeater rack. Due to action of thread screwing between a bidirectional screw and the nut swing link, the nut swing link swings around the axis of the nut swing link when reversing of the ends of the bidirectional screw is performed, and then the horizontally moving carriages are driven to move. The winding drum not only can rotate around the axis of the winding drum, but also can move forth and back along the axis of a carriage horizontally moving mechanism, and the cable arranging quality is improved.