The invention discloses a secondary protection device for a receiving plate of a ship unloader. The secondary protection device aims to overcome the shortcoming that if an existing
cam limiter arranged on the ship unloader for controlling steel wire ropes on a roller of a
winch to lift the receiving plate breaks down, the steel wire ropes will be snapped and the receiving plate will fall. A
rope penetrating frame with the vertical face parallel with the center line of the roller is installed on one side of the roller, the steel wire ropes penetrate through the
rope penetrating frame, and swing arms capable of swinging along with the vertical face are oppositely installed on the two sides of the vertical face, opposite to the roller, of the
rope penetrating frame respectively. The rope penetrating frame is further provided with a limiting switch, and when wires, wound around the roller, of the steel wire ropes move excessively towards the two sides respectively, the limiting switch can push the swing arms to
cut off power of the
winch. When the wires, wound around the roller, of the steel wire ropes continuously and excessively move towards the winding side or the releasing side, the parts, in the rope penetrating frame, of the steel wire ropes forcibly push the swing arms to be deflected towards one side of the limiting switch and to touch one side of the limiting switch, and therefore the power of the
winch can be
cut off, the accident that the steel wire ropes are snapped and the receiving plate falls is prevented, and secondary protection is achieved.