The invention relates to an improved hoisting tool for installing an inversely mounted full-rotation rudder propeller and the technical field of installation of full-rotation rudder propellers of ships, in particular to an inversely mounted full-rotation rudder propeller. The improved hoisting tool for installing an inversely mounted full-rotation rudder propeller comprises a laser seat, wherein acommercially available simple laser flashlight is installed in the laser seat, an indication plate with a '+' line and a concentric circle scale is installed at the center of the top end of the inversely mounted full-rotation rudder propeller. In addition, three to four guide plates temporarily installed on a structure seat frame by a traditional method are retained, and two to three large and small headed studs are screwed in mounting screw holes in the inversely mounted full-rotation rudder propeller body. The improved hoisting tool is simple in structure, easy to manufacture, low in cost,convenient to mount, simple to use and convenient to maintain.